I need help with LTW Income System

[SuperWC3Noob]

Hey can any one tell me what triggers and variables i need to use to make a income system like in LTW such as you spawn a peon thats +1 income then over like 15 seconds depending on the amount of peons you sent (example:10) your income would be 10 and it would stack etc. Who ever helps me i will give them credit in my map also