Denise, I have a 12' × 16' stand-alone Sun Glo greenhouse in Zone 6/7a for 25+ years and it has held up well. It is attached to a 3 ft high lower wall/foundation made of railroad ties that adds insulation too. You can also surround the railroad tie base with styrofoam sheets for further insulation. I thought about doing that but I think the railroad ties provide enough on their own and I silicon caulked all their seams so no cold air seeps in through the cracks. The railroad ties have rods going through them deep into the soil to keep them stong and well anchored during windstorms. I have a dropped door so I don't have to climb over the wall to get in. The foundation wall also adds height which is also valuable to have to keep temperatures stable plus being able to hang plants from the ceiling and allow room for our trees to grow taller. I also added thick aluminum triangular-shaped roof braces to the peak roof ribs which makes it very strong and stable. It has an aluminum frame. The aluminum parts have held up well, but any steel accessories rust with the high humidity so don't add anything steel and use screws or rivets that will not rust. It's "glass" is made of 2 layers of Acrylic; one layer is corregated and the other flat. The airspace between creates the relatively high R-factor. I added a layer of bubble wrap to the walls and ceiling after several years to provide further insulation. I think it saves on heat and still lets in lots of light. The "glass" panels have stayed clear after all these years. I have had no leaks or sweating (water condensation drips from the ceiling which can damage flowers and leaves) ever from the ceiling. That can be a problem in many greenhouses. I use 2 vented Southern Burner gas heaters and I set one several degrees cooler and it comes on when backup heat is needed on subfreezing days. These furnaces do not need an electric source for the thermostats to ignite the gas to come on which is good for remote areas when it is too expensive to run electricity to. I use gas from a pipeline to my house, but they make propane and natural gas ones that run from tanks too. You also need a backup heater that runs on a different fuel source than what your main heater runs on especially if you are using an electric heater and there is an outage or if severe weather might impede delivery of propane. You might need a battery backup if your igniter or furnace fan runs on electric. My greenhouse comes with an exhaust fan which works on a thermostat in conjunction with an air intake shutter system and it has 2 peak vents. The automation is well worth it on rapidly changing temperature days during early spring and late fall. I also use several regular fans 24/7 to circulate air to prevent fungus and insect damage. I also have a Hydrofogger to mist and provide humidity which also cools the inside by about 15°F in the summer. Spraying the floor also helps cool the air and provide humidity in the summer without using the hydrofogger. I actually have that for my humudity loving orchids. The citrus trees really don't need the high humidity. The air vents and the shutters are very thin so in the winter I cover them with insulation batting. On hot winter days I ventilate by opening the door window/screen, but that is not automated. I also double wrap the door in the very coldest part of the winter with bubble wrap. I can't tell you how much it costs to heat as my house and greenhouse use is combined, but I have a large house and my gas bill is not too bad; at least it is affordable to me. The furnaces rarely run during the day as the sun heats it up even on cloudy days. My floor is bluestone with a well-draining weed-free barrier underneath and I top that with those interlocking foam floor mats so it is easy to sweep out. Orchid bark is a bugger to pick out of 1 inch blue stone. The railroad tie foundation starts about a foot underground and seems to keep animals from trying to burrow under it to get in to escape the cold. I have never had weeds or rodent problems. The bluestone floor adds humidity and cooling as wetting it down on hot days will cool the greenhouse by 15°F. I originally decided to not use a poured concrete and block foundation in case I might someday want to sell my house and the next person might not want an old greenhouse in the yard. It also keeps the cost down significantly. I could easily take the greenhouse and wooden foundation apart and plant grass seed and no one would ever know the greenhouse was there. All my neighbors seem to love it though and it probably would be an asset to the sale of the house. I also ran gas, water, electric and telephone lines out to it underground through my basement wall. That adds greatly to the initial expense but is well-worth the convenience all these years. I have since seen heated hoses that maybe you could use to water and humidify without running a water line. I don't know how long it would last, but if the distance from the house is not that far it might add some convenience. I know someone who used one. I started growing orchids in my greenhouse initially by themselves for many years but then i really got interested in citrus big time and started moving them in. Now I have so many citrus trees there is no room for all of them and the orchids. Many I grow from the tree branches or hanging from the ceiling above the trees or on top of the trees' pots like Brian does which adds a lot of color. The rest are growing in a 15' × 20' basement room under t5 lights and on practically every windowsill in my house. I keep many of my tropical plants in that room such as hibiscus, tropical vines and fruits. It is like summer in my greenhouse and my basement in the winter. A tropical oasis. My advice is to build as large as you can afford and will fit in your yard as you will always want more space. I have toyed with the idea of extending mine at times as it does come with an extension kit. But as I get older I think a larger one might get too much for me. I thought about getting an attached to my house greenhouse vs a stand alone initially. I decided on the standalone after considering fire possibility, possible rotting of the wall between the house and greenhouse from high humidity and possible leaks where the roof attaches, ice falling on the glass panels from the house roof above, the house painter having to put scaffolding above the greenhouse to paint the house, the ability to possibly use insecticides or pesticides in the greenhouse that could possibly contaminate the home if they were attached as one unit, etc., etc. Lots of thoughts went into this decision. I thought it might be discouraging to have to go outside to go in the greenhouse, but that is not a problem or real inconvenience. I thought opening the door to get in might cool down the greenhouse, but it doesn't. These are things you need to think about though. I use an aluminet shade cloth. Much better than the black knit one i started with although that one was very well made. The aluminum seems to cool it in spring and summer although the reflective fibers provide more light and hold in heat in the fall and early winter. It is very light weight and flexible. I can almost put it up without a ladder. I attach a ball of rope to the shade cloth grommets on one side....throw the ball over the roof and yank it over the roof from the other side. You want to make sure there are no sharp things sticking up from the roof that the netting can get caught on. I hold it down with bungee cords with cup hooks attached to the railroad tie base. I only have to get up on the ladder to run the bungee through the grommets at the peak ends. To take it down I do not even need the ladder. Putting the bubblewrap on the inside of the roof was not so easy as I need to get up on the ladder and work overhead to tape the strips. I also use stretch curtain rods to help hold up the bubble wrap. It works well and has stayed up for almost 5 years now if I remember correctly. I am not looking forward to having to do that again though. Many spots are hard to reach like the corners above the furnaces. Many on this forum instead wrap their house from the outside with swimming pool insulated covers although did strap it down with bungee cords, but I am not sure I would be able to lift that over the roof by myself as it is quite heavy. My sister has been using that method for years and it makes a big difference in her heating bill has her greenhouse is glass. She also uses deer fencing over the pool cover and then ties that down to make it stay on her large attached greenhouse. It has never blown off. The bubble wrap I use comes in strips so it's not hard to lift but hard to tape overhead and get around and under all my hanging bars. It is tedious work but if you get UV bubble wrap it doesn't degrade very fast and I think the shade cloth protects it from the sun. I use 6 ft wide wrap around the sides in one piece to avoid seams. The roof pieces are narrower to fit between the ribs. Mine is a relatively cheap greenhouse kit that if you are handy you can assemble yourself with help. It is the labor cost of having one built that makes a greenhouse expensive and adding underground utilities. You will want to make sure you have temperature monitoring and alarm equipment in it as breakdowns inevitably happen on the coldest or hottest days, especially when you are away. These alarms can be simple to quite elaborate but can save the lives of your plants. I had a nice one that ran off my telephone system that would call my cellphone and two other backup numbers when the temperature or humidity got out of set limits. I don't have landline phone service now so I use the Temperature Stick that many others on this forum also use which monitors temperature and humidity and will send you text or email alerts via my internet service. The trouble with it is that I am not easily awoken by an email or text alert in the middle of the night as a ringing phone. There are also inexpensive remote battery operated alarms that you can use on your property if the distance is not too far. The phone and temperature stick alarms are as near as your cellphone. Many will also store data for you to download and analyze. Get as large a greenhouse as you can afford and can care for and fits on your property. You will have years of joy from it. You can add heat and cooling systems and other accessories to get year long use from it. I find it is best to add shelving and tables as you go as I am constantly reconfiguring mine as my collection of plants grows or changes. I find using wire racks set up on bricks, cement blocks, plant stands or whatever are best as they are easily changed out. Smaller lengths are easier to use for shelving and hanging bars as they are easier to work with in the cramped space than longer lengths. Don't spend too much on accessory benching as you will be changing it out to fit more plants in. Use what you have around for accessory benching such as large containers and smaller pots to raise plants up off the floor or over drainage trays. There is definitely a learning period to get used to your greenhouse but it gets easier. If you can, don't get the smallest greenhouses as they are not as easy to heat or cool, but if that is all you can fit or afford you will still have fun with it and get a lot of use with it. The small ones are hard to keep cool in the summer but you can use it the rest of the year. Another important thing that you might not have much control over on a small lot is greenhouse placement. I know I would get better efficiency if mine were on an angle on my lot so the sun would shine directly through the roof, but it would look strange on my lot. I would really love to have the better efficiency when I am growing things in the winter. You will be surprised how low the sun is in the sky in winter and how trees and houses way in the distance will cast a shadow on your greenhouse. If you are able to consider this it is worth getting it right. I am writing all this information because when I got mine I could not find any information and had no one to ask questions about. I will be happy to help you with any questions you may have with a hobby sized greenhouse like mine. There are so many things you just do not even think about until you are growing plants in one.

Cory