The first barn I put on my place was a corrugated sheet metal structured pole barn. At the top of the poles I put 2 ea. 2x6's, one inside and one outside to put the 3/12 trusses on.
I ran the wall tin up to the top of the 2x6's leaving a gap between it and the underside of the roof the height of the trusses at that point which was about 5-6 inches. I thought that this would be a real neat vent and keep the barn cool and dry. Ha!
The roof sheet metal extended past the the side of the barn 12" (overhang).
Not long after I built it a thunderstorm rolled in with moderate winds and heavy rain. I was standing inside about 3' from the wall GETTING SOPPING WET!!!!! When it stopped, I boarded up the open spaces (vents) between the trusses.
Point here is that you have to do something with your roof water to keep the wind from blowing it into the barn. Gutters is a solution as would be to build the soffit like a brick house where you close it in and put your vents on the under side of the soffit.
Forgot about that in my earlier reply.