I was looking into building a greenhouse at one time. I like how the plastic panels curve on that one. I was pricing the polycarbonate greenhouse panels......holy smokes those things are high!
I built a 14' X 14' Hoop House using 2 ea 10 ft. PVC lengths per hoop. I built using the 1st layer of 6 mil plastic, the 2nd layer of 1" fiber mesh and the 3rd layer of another 6 mil plastic covering. Ends were made from plywood and 2"X4" studs and plywood door. Not too bad of a build, however, it was not used much for the purpose it was built for. I wanted to have an aquaponics setup which never came to fruition, but I did use it to start some of my plants. Then it was taken over by several bags of fertilizers, soil amendments, boxes of coconut coir, fruit tree fertilizers, and various other artifacts of gardening.
It was still worth the effort of doing my own. I laid everything out full scale on paper and then started hammering and screwing the ends together. Once those were up and the hoops in place along the 4" X 4" bottom frame I had friends and relatives over for afternoon "tea" to do the covering. The filling of all the chemicals was all on my back!