Well, since I assume you main Fox, I don't have a lot of knowledge against him in general. I'll try, though.
You want to try to avoid Roy getting in on you in the first place. Fox has lasers, which would be very good against Roy since he suffers against projectiles, especially on FD. Lasers can also help you approach. Out of D-Throw, your best option is to jump, although you can be chased with U-Air. It allows for minimal damage and the least amount of follow-ups. Honestly, just keep away from Roy. Go in when you're absolutely sure you can get a grab or start a combo. Your best move is your lasers for basically everything as long as you have a nice wall going with them. Try to ask Fox mains as well, they can give you insight on the other side of the matchup (what to look out for, optimal options, etc.).