Yes, the jig was made on an improvised table with a couple of sheets of plywood for the surface. Blocks for the jig were screwed to the surface to define the curve and hold the ends of the convex side. Once I got into the rhythm, I could do a half arch in about 7 minutes, with two 3" galvanized deck screws through the strapping and into the each block from either side, so that the screw points overlap by and inch.
The tops are gusseted together with plywood. There are stringers on top to either side of the ridge, but no ridge board.
The frame was made with a lot of scavenged material for blocking and bracing, so I paid just $100 for the strapping and screws for a 16' x 24'
greenhouse, about 8 years ago. It's due for new plastic and frame overhaul now, but I'm happy with those 8 years.
I don't know about the more rigid materials to cover it. I've got another one with an east-west ridge that I boarded up the north side on. I keep my
firewood in there, and dry my laundry in there too. That one is on a pallet foundation, on top of plastic laid on the ground.