I'm playing as a monk, the DM agreed to allow me to use a whip as a monks weapon (think Shaolin monks using chain whips), but we aren't sure how to treat the hit/damage rolls, would they stack or should we disregard the finesse. I don't want a game breaker, but the rolls seem to get a little ridiculous sometimes. Monks dex is 16, +3 bonus to hit/damage
Finesse:
When making an attack with a finesse weapon, you use your choice of your Strength or Dexterity modifier for the attack and damage rolls. You must use the same modifier for both rolls.
Best Answer
Finesse simply lets you choose whether you use Dexterity or Strength modifiers when attacking. The monk weapon feature simply lets you apply the equivalent of this option to any SIMPLE weapon that is not two-handed or heavy. They do not stack in any way.
If the weapon already has finesse then that option is irrelevant. The monk weapon allocation would allow you to use the higher damage dice as your level increases.
In the case of your whip, you would add your +3 bonus from Dexterity to hit and damage and would roll 1d4. At level 5 that would increase to 1d6.