I was thinking of putting ply on on my shed roof, but what thickness could it take weight-wise if I was to fix it on top of the planks already forming the roof? And would this be ok? Shed is 8 x 10 ft apex. Having taken off the old felt, I found the sky was visible between each roof plank, ie the people I bought the house off, had not used t+g close together but with a gap between each one, surely this was wrong?? The roof planks are not even butted up against each other. Also they had put the felt on with staples not clouts. No wonder it was leaking. Can anyone clarify this please, I thought there were supposed to be no gaps! Thanks. First time on any forum so bear with me!