I intend to use ready made roof trusses but need to know how many , what thicknesses , best place to get em and things like battening felt and all the trimmings. I also want to be able to insert two velux roof windows. and my wife wants storage in the roof space. dont know if that makes a difference to the type of trusses. The dimensions of the roof are as follows lengthe of shed on apex side is 4.2 metres. and on gutterung side is 5.4 metres.