Leasa, I made a simple greenhouse by getting 1/2 or 3/4 plastic pipe,and bending them over bed and securing with the proper size pipe hanger. I secured one or two per side to bed,spaced about three feet apart. It isn't a real tall coldframe/greenhouse,but it works. Just cover with 3 mil plastic.To hold plastic onto piping,I used cheap plastic spring type wood working clamps. Good Gardening! :)

Thanks for the measurements that is sorta what I had in mind but was wondering just how thick the plastic should be and if 1/2 pvc would work.

Leasa-- You must use a flexible plastic pipe. 1/2 PVC will flex- Your best choice is either plastic water pipe,or plastic electrical pipe. Experiment with one piece first of either to be sure it's what you want. :)

I've use 1/2 inch for a coldframe and it wasn't enough, keeps breaking at the joints. I just used the heavier clear plastic drop cloths, but that only lasts a couple of years before needing to be replaced For a larger structure there are UV resistant versions designed for greenhouse use. There are instructions on the net for building PVC greenhouses, just pick one with dimensions that will fit over your bed.