Never seen a wood roof on any RV. Except maybe a few home built ones. Most current RVs have either TPO or EPDM roofs. For the discussion, just say rubber. Roof construction is generally interior ceiling material fastened to roof trusses, insulation, followed by wood substrate, usually OSB or plywood, with rubber glued on top. Most roofs will support 250 to 300 pounds, so generally safe to walk on. Roof trusses can be either wood or aluminum, with most higher end units opting for aluminum. Really makes little difference except in weight, cost, and reduced chances of rot if a leak occurs.
So, what is your real question?