If you go the traditional flat 2x6 route, they will be exposed - make sure you use nice looking wood. On my garages, I have made sure that the openings are framed solid on the sides and the top (make sure the sides run long on the top to receive the tracks). I then run 1x material on the jamb side and run it long to the interior to receive the drywall butted into it. The door tracks then lag thru the drywall into the solid backing. Makes for a cleaner look I think. Some will complain that the drywall will crumble over time and make the door mount weak - has not happened to me in 10 years running.