Free Greenhouse Plans
I've owned commercial-built greenhouses, and I have built and owned some from scratch. I believe the one I have now is about the best you can get for the money - for several reasons. It is the Mittleider Greenhouse, and it's in appendix D of the Mittleider Gardening Course, available at www.growfood.com. Several other of Mittleider's books have the plans. Consider the Mittleider Library CD, which has all of them.
The Mittleider Gardening books and Manuals teach all you need to know about this subject, and can be purchased in the Store section, or as digital downloads.
A digital copy costs 30-40% less, and is available instantly! I HIGHLY recommend you look here http://www.hightechhomestead.com/Products.htm for the best gardening books available anywhere! Get one NOW and be gardening TODAY!