See if there's a pattern to his dodges.
If you run at him, will he roll backwards? For some characters, it might be more natural to roll backwards/away from them. For others, it's generally better to roll forwards, and yet, for others, it may be better to just spotdodge.
If you think he's gonna roll backwards, then don't plan on attacking where you see him as you're running - plan to attack behind him
If you think he's gonna roll forwards, try a DPC (dash pivot cancel), or just run 'between' his roll length and starting point and turn around.
If you think he's gonna spotdodge, then try delaying your attack, or doing a run past + pivot grab.