#1 would be my choice. #2 interprets aerohead's suggestion, I'd like to see if he confirms it.
Maybe he will explain why having the peak be 30% back on the overall length is optimal.
Your constraint would be the location and size of the rooftop hatch opening. To preserve the bunks, are you going high-top or pop-up?
For material I like PolyMetal/Alumipanel composite sheet. Stiff as 5/8" plywood and prefinished.
