A new question came in about how to build a small green house inexpensively.
A hoop house is usually recommended as a small project greenhouse. Take a look at the listings on this link at Build It Solar. Lots of possibilities there.
Also, check the library. There are several do-it-yourself books with plans for basic greenhouses.
Some long-time gardeners think that with global warming, a home gardener only needs a simple cold frame unless you have your heart set on a greenhouse. There is a set of instructions for a raised cold frame at Ron Hazleton's site. Click here to see them.
If you can't find what you want at the library or online,
The Noble Foundation in Ardmore has a DVD with instructions on how to build a $500 or $600 hoop house which is the minimum they cost to construct.