The Internet Archive (Archive.org) is a primary resource for finding complete, verified ROMsets for specific MAME versions.
The app should automatically scan the folder and list your games. If a game doesn't appear, tap "Settings" "Refresh ROM list." Some games (like Donkey Kong ) require sound samples. These files should be placed in the /roms/samples Troubleshooting Game won't start: mame4droid 0139u1 roms archiveorg install