If you are looking for a secondary, you should look for a character that will actually help you address your main's difficult matchups. As an ICs player, you'll have a lot of trouble with Peach and Fox (maybe Marth/Falcon too).
Right off the bat I'm going to tell you that Roy is pure trash in those matchups. At best you'll have Fox on FD as a CP, but that's still heavily in Fox's favor. Peach also absolutely destroys Roy. In the neutral, she'll treat you like Marth with turnip camping, but when you do finally get in, you'll get maybe 15% off of your combo or you'll get CC Dsmashed. You'll also be punished ridiculously hard.
I would highly suggest picking up a different character for a secondary. Do not listen to Roy's who claim that he is viable in any top tier matchup (request video footage of them playing high level players and winning if they claim this). I would strongly suggest picking up Marth, Falco, Sheik, or Peach as a secondary. You could also work on Fox, but you may be better off just learning one character than trying to pick up a secondary spacie.