Roy 101:
Dash dance grab something (Sheik, Ganon, Link, whatever)
Throw and force techs however many times necessary to get them into a vulnerable position, mix side-B and d-tilt where necessary but focus on throwing them to force techs that you can chase on reaction
If you're slow to react then make sure you space to avoid their counterattack, combo break option, or whatever (or bait it with dash dance, or wait for it to miss and then hit them - they all work to some degree)
At some point F-smash on a tech stand (at like 40%+, ideally not across the stage but in a spot where they go offstage)
Edgeguard with stuff - his edgeguard is decent
Repeat until you've won
I summarized Roy's best combo vs non FFer / non floaty and best strategy in neutral in one post w00t
Floaties are lame though
Vs them just DD camp and grab, sword them in the air when possible with your poking sword moves (fair, side-B, jab, uair, etc), try to grab them if they land and escape the combo (or if you're not confident in the poking thing) and expect the game to take 5-7 minutes unless you cheese them or get cheesed yourself
Roy just tries to make up for all his weaknesses through ground control & positioning & out-ranging people. It's lame but sadly better than GAW (at high level; lower & mid level GAW is way better than Roy at that level).
If they platform camp with a heavy then switch to Fox if they get a lead 'cuz that's lame and gay. Or go FD.