The table is flat, but the drywall will even out any minor sags. If you have any doubts, you can use a straight edge or a 4' level to make sure your table is flat enough. You don't need a saw to cut dry wall. just a straight edge and a good utility knife will do the trick. They make a "T" square for drywall that makes this even easier, but you can use a metal ruler, a level, or any other suitable piece of metal as a straight edge. Use the straight edge as a guide for the utility knife and all you have to do is score the drywall 1/4 deep and break it off. It will break off nicely where you scored it, you may have to make a follow up cut through the backing paper if it doesn't tear off or break clean through.