Here's my roof structure:
vertical 1x2's interior, between the walls
layer of 1/8th inch plywood glued and stapled to vertical 1x2's... plywood goes outside wall to o/s wall
horizontal 1x2's glued and screwed through plywood and into interior vertical 1x2's
next I'll put 3/4" insulation between the horizontal 1x2's and cover the whole thing with 1/8th inch structural panels and then aluminum.
The 1x2 running the length of the outside wall is glue laminated lattice bent to the curve.