I've done it. Polycarbonate is better than fibreglass (even in strong winds).

Whereabouts do you live?

Innisfail, Canada

We get lots of wind here during summer, so my greenhouse does need to be strong .

polycarbonate is strong. It's usually the anchor points that fail. If you use screw through attachments at the recommended rate you should be fine.

Yep,

I built my own out of wood. Can't even put a shelf up straight but managed to put together a 24ft x 14ft structure on my own.

Yes you can go with plastic, it will stand up to the winds OK if you secure it correctly. Using a double poly covering will also mean you don't have to be as accurate when building your wood frame.

What I did was save my money until I had $700 and then ordered a truck load of 2x4s and plywood and cement blocks. The roof slope is 30 degrees and so I only had to cut 30 deg and 60 deg angles.

The reason it is 14ft wide is that with 30 deg slope the roof panels are 8ft. (so are the 2x4s)

I built it with sidewalls of 6ft so that the bits I cut off the 4X8ft ply for the solid north wall became the 2ft kneewall on the south.

I didn't need the greenhouse so high, but the master plan is that it is extended as a structure to 56ft long, the last 18ft being a garage. (seperated internally and different roof and wall coverings)

As to wind..... well the poly covering survives the wind OK as long as you secure it OK.

For very high winds in summer I turn on the exhaust fans and block off the intake and the greenhouse "shrink wraps" itself. No destructive flapping. In winter the poly is so tight wind doesn't affect it.

I built my structure with the intention of covering it in polycarbonate. All the strut spacings are set up for it. As I get more money I will polycarbonate it, the roof is going to be first.

OK pictures.

Before, you see the length of the old chicken shed.

http://www.stormlakeonline.com/user3316/2.jpg

The structure (part one) built.

http://www.stormlakeonline.com/user3316/picture_0008.jpg

Notice the blue and white tubs on the ground? They were tomato and pepper plants the wind took down. Also notice how 5 panels on the greenhouse look patched. Yep!!! shingles from the barn and corn stalks from the field took out the poly on those sections.

Enough of my rambling.... build the frame well, use windows on the bits where you want to see out, polycarbonate or fiberglass on the roof and plastic on the rest. Unless you are really rich, then get that triple wall polycarbonate.

Chris Thank you for your input, you have given me a few great ideas .
Your greenhouse looks very good ( would look good in my yard too *LOL* )
I guess I go back to the drawing board to implement some of your ideas . ( unless you have copyright on that )

innisfail,

No copyright on anything I do. However I CANNOT send you any construction plans. *LMAO* I didn't use one or draw one! Sort of roughly worked out how many 2x4s I needed and went for it.

Wood is great to build your own custom structure with. If you get something wrong you just nail on some more wood!

Being totally honest with you, when I built the frame for mine I didn't really know if a greenhouse here would work so I covered it the first year, and the second, with cheap construction plastic. The idea was if I didn't like it or use it then I could cover it with galvanized sheet metal and I would have a shed.

Now it has a covering of professional greenhouse poly (double layer of course as I am a professional now) exhaust fans, and all the benches and shelving stuff, and misters and thingies.

This fall project is to build a SHED with real walls and a real roof so I can put the mower in it!

innisfail, go for it!

Well I AM GOING for it .
Just checking lumber prices ( get better deals at auctions here locally, most of the time ) and that makes a differance

I am a person that will make a "blue print" just to double check, but it will be a rough sketch .

I will probebly work with 2x6's or even 2x8's because of that darn wind ( only 2-3 storms a year but they can cause a lot of damage )

I am so looking forward to this, "luckely" winters are long here so I have some time to put it together in the garage .

innisfail,

Also you will need a wireless router, I have a motorola WKT850G Wireless networking kit.

Also you will need an old computer. One that does not play all the latest games but can still access the Internet. (to be honest when I was transplanting last spring I watched "Hunt for Red October" so many times every time I see a small plant I think submarine! (note to self, take more DVDs out there!))

A coffee maker,

A beer fridge, (a cooler and ice works OK)

(Microwave optional)

Currently I have nothing plant like in there, this weeks project in the structure is fixing and re-painting the storm windows for the house.

Wow
You make it quite entertaining all that transplanting .
I am always sitting at the kitchen table, with the radio on .
Since winter is coming, all my few plants are in the basement, trying to handle the weather .
My first tree seedlings are gone stay outside, hoping they survive the winter .