Seller-Financed House Hack

[Joshua Stewart]

I am a designer-contractor. We are currently renting our friend's house through the end of the year while he is out of state. When we move and he returns he is leaning towards either selling as-is or rehabbing then selling. We are considering a proposal to renovate the house ourselves while we live in it - we would cover construction costs, nothing out of his pocket, while we continued paying rent. The mortgage would stay in his name, so it would be seller financing. Let's say we agreed to give him his asking price of $100,000 as-is. Could we then have our agreement be that he keeps the agreed upon $100,000 ($85,000 owed on the mortgage + $15,000 profit) and pays us the difference, thus reimbursing our construction costs and giving us profit?

Thank you in advance to anyone who replies!