So I am trying to figure out what to do for the roof of my cabin. The cabin will be 20x24 with 12/12 pitch roof. I am going to use rafters made out of 2x10's. The questions I have are how should I vent and insulate the roof? I plan on using metal. Do I sheet the roof with OSB or put the metal directley over the rafters? With the 2x10's have enough room for insulation or should I go with 2x12's. I was thinking about putting 2x4's horizontally across the rafters a couple feet down to make the inside of the cabin have a flat cieling, would this be a good idea for ventilation and insulation?