VENTING AN INSULATED ROOF
You'll need to install ridge vents, soffit or facia vents (depending), and install Soffit Chutes. In short, you DON'T want to apply insulation directly on the underside of the roof! You'll just create major problems!
As to how to do all this, I'll leave that up to you to find out. (I can't do it all for ya ...) My best to ya and hope this helps.
Jay J -Moderator
PS: God Bless America!