You can have 3M clear adhesive (clear bra) installed on the ENTIRE body surface of the car if you want. It was about $400 to have the following done on my 5'er - I have the hood, front bumper, front fenders, and the back of the mirrors done. Only problem I've noticed is that since my car is white, the clear bra tends to appear "yellowish" ever so slightly under the right light. For any other color car this shouldn't be a problem.
Any reputable shop that installs the clear 3M film should have no problem doing the roof as well.