I have a 50's Trilevel that needs a porch repair. It is covered, about 24'x6' and above a garage (in Chicago). My plans are to rip off the old carpet/roof membrane/ sheeting etc and replace. I plan to have the porch surface on sleepers on the roof membrane and then covered again with membrane. I would then attached the wood or PVC to the sleeper. Would tongue and groove Cumaru be acceptable in this situation? The sleeper will only be about an inch thick and will not allow a lot of air circulation, which I have read can be a problem. How important is air circulation in a covered t&g porch? Would PVC be a better choice? How much does PVC expand/contract? Has anyone used Larch for this purpose?