Building Greenhouses
- Build a Very Simple PVC Hoop Greenhouse
- Inexpensive and Easy Greenhouse
- Build a Simple PVC Hoop Greenhouse with End Doors
- Build A Small Backyard Greenhouse
- Build an Inexpensive, Easy Hoop Greenhouse
- Build A Simple, Rectangular PVC Greenhouse
- Plans for a 32' x 10' x 10' Greenhouse
- PVC Hoop Greenhouse
- Buildeasy.com Do-It-Yourself Greenhouse
- How to Build a Solar Greenhouse (Cold Climates)
- Simple, easy Greenhouse
- How We Built our Passive Solar Greenhouse
- Building A Deluxe Greenhouse For Cold Climates
- Easy, Sturdier Greenhouse from Cattle Panels
- Hog Panel Shelters
- Huge, Sturdy, Plastic-Covered Building
- Planning and Building a Greenhouse

Image from http://westsidegardener.com/howto/hoophouse.html
You can buy truss kits for garden sheds that attach to 2x4's and make an almost instant frame to cover with plastic. Voila - you have an instant greenhouse for about $100 depending upon the grade of wood and plastic that you use. If you recycle wood, it would be even cheaper.