I keep seeing over and over people touting their 3/8 roof. How about the rafters that are 1.5x1.5 inches thick. When I had to redeck my trailer I doubled all the rafters before putting the new plywood and roof on. When taking the old decking off the only rafters that were doubled was where the A/C goes.
My personal opinion which matters little. If your a fictional 150# person you should have no trouble on the roof. Any more and you risk damage not so much from the plywood but the rafters under the plywood.