Need help with my first flip

[Mohammad Zahid]

So I've been highly interest in investing in real estate for quite sometime now. I've watched numerous podcasts, read many books, I even passed my real estate exam to become an agent. After looking around for deals I came across an opportunity, I just don't know if it's a good idea and how to go about it. The deal: I found a owner vacant house. The owner of the house offered me to fix up the property using my cash, and then flip the property and from the profit give him a small share. So basically instead of buying the house from him and then flipping it, I fix it up and then pay him for the property. Once it's flipped I would then pay him $375k for his asking price and an extra 10k from the profit and I would keep the rest. My question is how can I make sure that he doesn't change his mind once I'm done fixing it. Is there a way we can notarize a document in which he is obliged to give me the remaining profit. Or for him to transfer the deed to me without any money but have in writing that he will get "x" amount when the property is flipped?