Looking out for a devon side elevation roof that reasonable priced for my self.The base frame is moulded fibre glass that holds the bed boards and sits the roof bellows on.This might be a problem to reproduce to do the same in wood.
All you need then is to lay up a timber base around where the roof bellows fold.Then offer up the frame to the tin roof .If its being cut you can make some folded 90 degrees sections to screw into the wood frame.
