Lag makes everything worse in this game so FG is probably never going to be a very legitimate competitive environment (also FD only no customs, really limited version of the game but not relevant to your question). Rolls are very hard to react to in lag so expect worse results, but mostly they are rolling away from center stage and backing themselves into a corner. When they have nowhere left backward, they either roll into you (easily punished; I like dsmash with most characters) or do something other than roll with their backs to the edge which gives you lots of options to punish. There are a lot of specific punishes for roll away too; most dash attacks timed correctly can catch a roll away with a pretty weak read, Charizard eats them for lunch with Flare Blitz, throwing projectiles can be a strategy to make rolling away really unrewarding, etc.. Just remember that while they are rolling they are stuck rolling until they're done and are putting out no hitboxes that entire time while you're free to act; either seize a positional advantage or beat them to the roll's endpoint (which is fixed from the moment they start the roll) and drop a hitbox on top of them.
