Is there an advantage, especially insulation advantage, in leaving an airspace under “agricultural metal roofing” or corrugated roofing? We have put this type of roofing over plywood and tarpaper, and also on skip -sheathing depending on insulation options of the roof type (standard framing and timber-framed with finished wood ceiling. Denting is not a consideration. What do you think? Thanks in advance for your help.