I actually did this once to a model A ford roadster that I had purchased, which someone had welded the doors shut on, before I got it. I built a framework out of 1/4" steel rod that picked up all the lines that would normally show up in a fabric model A roadster top. The rear section that sat directly on top of the roadster cockpit area was made from 5/8" steel rod, which was heated with a torch and bent to follow the exact curvature of the body. The 1/4" rod is easy to work with and can be bent "cold" by hand. I had a friend who worked in the machine shop at the company I worked in machine me a set of "split hinges" that bolted to the "daisy panel" directly behind the cockpit, and bolted to 2 tabs welded to the round 5/8" bar that wrapped around the back of the cockpit area. The 1/4" rods which defined the top shape were attached to a home-made header that bolted to the top of the windshield posts with a pair of draw-down brackets similar to those on a good quality toolbox. The 1/4" rods were covered with a fabric padding material, and the top upholstered with canvas. This top was not a folding top. When you wanted into the car, you flipped the top open by lifting the front of it and folding it back on the hinges, untill it rested on the daisy panel, more or less like a crocodile with its mouth open. You then climbed into the car, reached up and pulled the top down (it wasn't very heavy at all), then snapped the draw-down latches into the locked position, and drove away. If you wanted to go driving topless, you just pulled the hing pins out, set the top aside in your garage, and left it at home.