I feel the 1st thing you will have to find out is what the building codes and set backs are in your area. Even associations have extra rules too. I my self when I owned a home had a pre-made garden shed 12x14 feet brought in on site. Then I had it wired for A/C etc. I used it only 3 seasons a year. I added a large window in the back for a view and painted it all off white inside rafters and all and created a country french dining area & daybed area and my whole family loved it. No TV or phones allowed. lol It was a great little haven. You do have to have it leveled properly and that would be the only extra cost of a prefab. I did the window and painting DIY Over a day you have a space ready to finish the interior your self or hire that done. Prefabs were 1/2 the price of stick built when I bought mine. The Amish in this area of IL where I live do fine work and build garden sheds off site. Then deliver them ready to go.