Help with tribute and triggers

I am trying to work a trigger for the campaign I am creating, and I want to get player three to side with me after giving 500 (stone) to it. How do I do that?

I suggest you to ask these kind of questions in II - Modding - Age of Empires Forum. That part of the forum is for these kind of question.

I dont have much knowledge about triggers, so i cant really help you.