Central NY Leatherstocking Region | I've done it both ways with good results. If you use purlins, be sure you close the ends up between them, or you'll make a good home for bats. You say its's steep - if it's too steep to walk on it's not an issue, but any metal roof you can walk on I put the purlins at 16" centers, so you don't bend the metal if you step between them |