I made a simple little tunnel that might be of interest to you. The frame was made with 5 pieces of 1/2 or 3/4" x 10' PVC, 2 lengths of 8' 2 x 3, 2 lengths of 4' 2 x 3, and a single 8' length of 1 x 3, and 4 lengths of 8' 1 x 2. Basically, I drilled 5 holes through each of the 8' 2 x 3 pieces, and a hole through the ends of the 4' pieces. These holes are designed to allow the ends of the PVC to go through them and be pushed into the soil. The 1 x 3 is drilled for the PVC to go through as well and acts as a ridge pole. Two 1 x 2's are used to staple to the plastic where it will touch the ground on the long sides. the other (2) 1 x 2's are used to provide support and stability as well as a place to attach the sides when you roll them up to access the interior for harvesting or tending your crops. This unit will need to be stabilized with cross tying to keep it from collapsing in either direction. You then put your plastic over the frame. I have yet to figure out the best way to close in the ends. I settled on using rip-stop nylon threaded over a wire frame, but you might also try using plywood. after using this unit for several years, I built a green house out of cattle panels. There are a lot of good instructions on the web for completion of a cattle panel green house.
Were you reading about Elliott Coleman? I'm in Maine, about a 1/2 zone further north of him, and my cattle panel green house has been fantastic. It will keep stuff growing until mid November, and stuff will start growing again mid Feb. currently, I'm using hay bales for grow frames, letting the chickens use the cattle panel green house this winter for a sun room. I go through soil withdrawal as soon as the ground freezes.