Greetings and Welcome!
I can envision one heck of a cab over camper on that rig. If you don’t want do a factory slide in camper, I’d look into the “foamie” camper construction methods. Lightweight but strong.
I’ve helped on a few laminated bond builds too, where you glue your exterior to foam insulation and then to your interior paneling. No ribs needed. Flashing for all the interior and exterior connection joints. Also lightweight and strong.
Windows are your friend, and eliminate the need for leaky roof vents or any other holes in your roof. A couple of opening windows and a ~$20 fan will give you better ventilation than two ~$200+ roof vents. Done right, the windows can be rain proof as well.
I would give serious consideration to a pre-built one, here’s 3 of them in your area:
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