Instead of installing plywood sheathing, roofing paper and shingles, I put together a video shows how solar modules could be attached directly to the roof trusses.
Since you have to install a roof anyway, the labor cost of installing the solar modules is essentially zero. Attaching the solar directly to the roof trusses also avoids the furture maintenance costs of having to remove solar modules that are mounted on top of three-tab shingles that need replacing every 15 or so years.
I picked Silicon Energy's solar modules because they are one of the few (only?) modules that are built to 4'x4' nominal dimensions. They are also glass-on-glass moduels which makes them extremely strong and very durable.
I do not have any financial interest in Silicon Energy. The design I show is a theoretical design using an actual Silicon Energy module. To my knowledge, Silicon Energy currently does not have a gap seal design that would be water tight and bolt directly to the roof truss like I show in the video. However, I don't think it would be too hard for them to do.