A little update.
We finished the roof plywood this past weekend. What ended up working was draping steaming hot towels over the plywood, then gradually bending it to shape over the roof frame (with plastic tarp between the new wood and the old wood/steel frame). I put a little boiling water on the towels several times over a few hours to keep them damp. After each piece dried for a couple of days, they kept most of the bend when the strap was released. It was quite easy then to glue and screw them to the frame with no cracking.
We have started on the bellywrap. We are using the same aluminum sheeting as the walls, 0.062 5052 alloy. It is held onto the steel base frame with Sikaflex 252 which is kept to a uniform thickness of about 1/16" by spacing with nylon tiewraps. We may get the belly coated with truck liner like Rhino.
Still undecided what to put over the plywood on the roof. We have recently read about a new Rhino coating called eco-coat, which has some aluminum particles in it. If I find that it is flexible enough, it could be a good candidate for coating the plywood. This seems like it would make a tough roof that you could just ignore for 10+ years.
