I haven't made a greenhouse that way, pdq, but have done that on a small scale to make grow tunnels. I also made a small 3 x 3 cold frame that I could simply lift off the plants, then sit it down over them again. I used t and elbow fittings and lengths of pipe cut to the distance I wanted between hoops to make a rigid base. Worked pretty well once I realized I needed to tape the joins to keep them from popping apart when I lifted the frame.

Thanks for the link to that site. I'm gonna go explore it further.