Structuring Unconventional Deal

[Marek Berry]

I'm seeking input on what the BP community thinks is a fair fee for my role in facilitating a transaction. 

The seller owns about six empty lots in TX in a desirable city. He's sold five of them and is also acting as the builder of the homes that will go on the lots. He's offered to "sell" me the last lot and he would build then sell the house + lot (it's essentially a loan to him so he has some capital to play with since it appears most of his is currently tied up). The return amount will be agreed upon before the deal is closed and will be a dollar amount, not a interest rate. He's a family friend and I trust him, plus he has significant experience in real estate.

I don't have the funds to do the deal on my own but am working on finding an investor.

Would you, the BP community, structure your fee based on funds invested OR profit once the deal is done? And what would you set as the fee? I understand 3% is a common finder's fee, but this also feels like a unique situation that could allow for a different structure.

Thanks!