The metal roof, on own barn does not have plywood under it. It's not necessary. The corrugated metal panels are nailed overlapping each other. Maybe we aren't thinking the same thing.....but here is a diy link.. http://www.wikihow.com/Install-Corrugated-Roofing
So sorry....I c/p the wrong thing. Here is the one I meant to add. http://www.homedepot.com/p/Suntop-4-ft-Castle-Grey-Wall-Connector-109290/100660867#.UdhNKjuTicw Not sure if this one or the strips would work best. If you go to Home Depot or Lowes ask. We have used the strips on a small...
Would something like this help? http://www.homedepot.com/p/Suntuf-24-in-Horizontal-Plastic-Closure-Strips-6-Pack-92770/100067957#.UdecTTuTicw Lowes has them too.