I built one from five cattle panels and built wooden rectangular center supports that I drilled a few holes and wired everything together, so sides are one panel high, sloped roof one panel, and a flat top, one panel. It is 16' long and 142" wide and the center of the wooden supports I could just walk through (I am 5'5"). Spouse at 6' hits the top flat panel. The ends have some cut up panel bits to fill in, and the far end had a hole for two 20" box fans. It was ground stapled along the long edges, and covered with 4 mil sheeting, held down with
concrete blocks along the edge. This was not enough to hold with two milkhouse
heaters against 25mph wind and 20f, so I had to string an inside layer of sheeting that didn't touch the outer. That gave me enough. That thing survived two years with snow of 8" and against 15f temps (and I built a windbreak for the issue with wind). Only thing is the sun would fry off the plastic at the joints so I had to replace plastic twice a year. Your version is a little smaller but it
should hold fine. If you are not getting enough insulation you might have to do a dead air second layer string in. Your form looks fine for snow and wind shedding, but you might need an additional windbreak.
2016 I moved the frame set across the
yard, made it longer, and wider, and turned it into a screen house covered with 30% shade cloth. It made the move by taking the ends off, unstapling then moving it like an inch worm, advancing the frames on the ground... Mine cost about the same and my door wasn't as fancy.
Thank you for sharing about yours. I will dig and see if I have pictures of mine while it was a greenhouse....