well it all depends on your goal... spl ,, sql or just plain sq... consecutively each one requires less,,, for spl you would want to do the complete car,, with more than just one layer,,, put it this way,,, this is a lil extreme but i have a friend whoes trunk lid weighs close to 60lbs,, all from raammat.. this is his webpage,,, and believe me you cant hear not one rattle nor resonation from anything,,, always a pleasure to listen to his car,,,,
he competes in sq class
http://www.cureline.net/lex/photos/a...l_progress.htm
to answer your question,,, you can do 2 rolls for the entire car,, or you can do a roll for each door and also a roll for the ccieling and also a roll or 2 for the trunk,,,, in most extreme case ofcourse,,, ,, i have one roll that i have used on my doors and my trunk,, and i still have about 1/3 if not more left over for anything else