Back in the late mid 70's I became obsessed with plants, specifically tropical plants. (I live in Iowa). I built my first green house in an "L" of my house just a small lean too. That rapidly filled up with ferns (Staghorn) and others. I out grew it. My next was a used greenhouse that I bought from the estate of a man who reitred from Chicago to Traer, Iowa. He had been the Chief Orchid Grower for the Chicago Conservatory. His hobby greenhouse was a 50'X25' All Glass and Redwood house with hot water heat for his personal Orchid collection that he brought back to the family farm when he retired.
I bought his house and moved it 20 miles and re erected it and got the wild hair to go into business just about the time the KMart decided to start trucking bedding plants into Iowa by the Semi Load, they could truck more in, in one load than I could grow.
My third greenhouse was a all glass breeze way between the house and garage. 44'X20'.
My forth was a lean to at the end of the above garage. Also all glass. Other than the commercial one I bought and moved all mine were built by myself to my design.
My 5th was a lean too with an all double glazed lexan skin and by far it was the best. This fall after I finish the addition to our cabin, I will build my last (I hope) greenhouse it will be Western Red Cedar salvaged from old telephone poles and double glazed lexan skin.
See the small greenhouse build by Norm Abraham on the New Yankee work Shop on line.
Mine will be 20-24' long and 12'-14' wide. All in all it has been fun. I would recommend that you build a small one just to learn (See Norm's) It could be used just for starting seeds and cuttings. Build then your larger display house for the beauty of it.
I second Jonathan's recommendation on FarmTek. They are only down the road from me about 40 miles and they are a good company to do business with.
Tom...