it comes with experience i guess. theres only so many times a guy can do a predictable move before he gets... well.... predicted. unless youre really slow, youll catch on.
but there are several ways i guess. if he is trying to roll past you, you can react quick and wavedash backwards for a hit. if hes on the ground you wait to see what he is going to do. if he does a hit, just shield grab otherwise chase it and grab again. maybe you can chase with a SHL into attack or something. there are too many ways to punish rollers. the fact of the matter is that its a predictable move and as your falco gets faster, youll be able to punish rolling easier
another thing is, if youre getting owned by someone rolling alot you are definitely doing something wrong. rolling is slow and predicatble and unless youre using the laggiest possible moves, i dont see how you are losing because of a rolling enemy. this shouldnt be too big of a problem once you master the gun.