PolyNome has a built-in polyrhythm creator.

Simply tap the + button on the main page and choose New Polyrhythm.

You can choose the polyrhythm on the left and some options on the right, the tap "Create".

NOTE: The polyrhythm will be created and saved as a preset named "Polyrhythm". If you create another polyrhythm, it will overwrite whatever is in that Preset. If you want to save your Polyrhythm, tap the Preset name menu and choose "Duplicate".