Master Roshi may have the Kamehameha wave, but Ryoma would simply knock it back at him with his tennis racket. Ryoma would then speedblitz him with his incredible speed and put an end to the match with a solid punch. Master Roshi would be on the defensive for the majority of the match and he would be rendered helpless. Ryoma wins.
Update 8 7 2020 Roshi is still a DBZ fighter even if he is one of the weaker ones. He won’t be able to claim victory here. Master Roshi wins.