This post came just came in from Ian Hart of Root Up Veggie Farm. I'll let him take over:
Last year I built a small hoop house for starting plants and after a year of use I can say it is working well. At 12x20 its just barely big enough for our 1 acre market garden. Its double walled and inflated with a small fan that pulls in outside air.
Here's a slideshow of my work:
I wanted to build a hoop house that we could move to another property in the future and that did not use PVC. I wanted it to last a long time and be able to support a moderate snow load.
I used 1 3/8" chain link fence top rail and bent the pipes by hand using a home made pipe bender really similar to the one featured in Off Beet Farm's Ruminant submission but with a 4.75' radius. The curve was cut out of a length of 2x8.
I found it really important to taper the ends of the anchor pipes to get them to be solid in the ground. The anchor pipes are 1 5/8"
The chain link pipe was purchased at Tri-West Fence and Gate in Kelowna for about half the cost that local building supply stores were charging.