I am doing some detailed research now for a plan to convert a used school bus to a tiny home.  I would like to raise the roof on the bus so that there is more head room, room to run conduit and room for about 5" of insulation.  The base dimension of the bus will be about 8'x40'.  The top will be raised by about 12" in the front third of the bus 14" in the middle third and 16" or more in the rear third  I also would like to have a recessed area in the top to put solar panels, recessed so that they can be flush mounted and not ripped off by highway speed winds. I will be installing a new steel frame in the roof, that connects to the frame in the wall of the bus, so the top is going to be heavily reinforced. Still, I expect to be able to have a couple of people walk on the bus to do maintenance and cleaning. The bus will be outside in the elements about 70% of the time, garaged only about 30%  The picture below shows something similar to what I want to do, only the picture shows a van with a raised roof.  I want to do the same thing to the whole top of a school bus.  The picture  below that shows someone attempting to raise the roof of a bus using steel.  I would like to use some kind of composite to create a smoother look yet having something just as strong and possibly lighter.  What materials would be easiest to work with and most suitable for this kind of project?