Contractor asking for a bonus

[Andrea L Eskew]

I'm a new investor working on my first flip. I've got a contractor who asked if he discounts the labor up front, if I'd give him a good bonus if the house sells for a lot more, so I would give him more work on additional flips. Originally we were going to fix up the house and sell as it is, size wise. But he said we could add a bunch of space, which would significantly increase the value and make us a lot more money. Having run the numbers, I would say he is correct. What sounds like a reasonable amount? A set dollar amount? A percentage of profits?