Roy is a thing of beauty. He is fast yet he has a really nice weight to him giving him a very specific level of friction with the ground. The most important thing when changing characters, especially with one like Roy, is to operate him around stages until you're incredibly comfortable. Learning to short hop with him, playing with his speed and recovery, and quickly transitioning with platforms develops this comfort. His range is a little short, but you need to use this agility to your advantage to make up for it. Short hop nair (as it is on many characters) is a great tool, its practically the bread and butter. It's short, auto cancels(I'm assuming purely because Marth's does usually), covers a large radius in front and behind and its one of his greatest tools for approaching. It also combos well into other aerials and can create easy juggles other of grabs. Compensating for the range is key when making a transitioning like this.
Rolling is a good tool, but Its one of the most predictably applications of movement in the game. People who see you roll will learn to punish it. Its good to roll occasionally, its a simple get away. But its also important to explore his options (use that speed!) of running, pivoting, etc.
Luckily the heavy reads that you'd do with Ike's still exist with Roy. That neutral b is a force to be reckoned with by all means. Also, the spikes function very similarly so that should definitely stress getting comfortable with his jump height so you can develop that skill set too.
Try to be a bit more specific with asking for Roy tips, I don't mind helping.