There are a lot of ways to build a simple greenhouse, some are more expensive and last a long time, some are cheap and last a season.
This one is more of the first. if you want one more geared to the latter, I have a video of a $100 greenhouse below the download.
I have always wanted to build a greenhouse, but I want mine to be underground and earth sheltered. so my overly complicated ideas prevent me from actually getting it done.
I really should make a PVC hoop house or something like the video below.Simple Gifts Greenhouse