You can get some nice kits, depending on budget. The polycarbonate somebody suggested above better than glass in a lot of ways. It insulates better and is easy to work with. There's a reason why you don't see commercial greenhouses using glass anymore.
Having said that I have (6) 4x6 foot glass panels from old storefront windows I plan to use for a greenhouse. They are heavier than window glass, and they were free.
Having said that I have (6) 4x6 foot glass panels from old storefront windows I plan to use for a greenhouse. They are heavier than window glass, and they were free.