Picking a player based on a percentage?

I think games like murder mystery do this. How would I start this or go about it?

Each player could have a hidden value (int value?) with a certain number (from 0 - 100). The value could be inside ServerStorage so the percentage of becoming sheriff or murderer stays when the player leaves and plays later. You could then run all the player's values through a code to determine who has the highest percentage.