Windows Charge Time system (for deciding turns in an rpg)


I'm making a tactical RPG in the vein of Final Fantasy Tactics. But I can't wrap my head around how to decide who's turn is up. I want to use a CT system (like from the aforementioned game) where everyone has ct and when you have 100 CT its your turn. The player would only get 5 units and for now the ai would only get 5, but I would like an isometric system so that I can add more/less monsters or have the player use less than five characters