Insulating a carport closet
 

I have a 10' X 20' carport closet that I am converting to a small workshop.
I want to insulate it properly. The carport has a flat roof that doesn't
leak. I plan on putting batten insulation in the walls r13 for 2x4s. and
r30 between the 2x10 support beams in the ceiling. Do I need to worry about
a vapor barrier creating a problem in the roof since there will be no space
between the insulation and the roof decking? I live in southern oklahoma
where we have very few days below freezing and it is very hot in summer so I
don't even know how much of a problem condensation is in general. Any
advice would be appreciated.

Thanks

Marc