Partnership with seller to flip house??

So I’m sure this has been done before, but I really don’t know how to search for it. I am preparing to offer on a property with a seller that is interested n creative deals. Seems to have owned only one rental which he got stuck with in 07. Very smart guy, and based on the conversations I’ve had with him he could be great to work with. Anyway, numbers and details look like this... Arv: 150k Repairs/cleanout (house is currently rented on month to month, would give notice tonvacate): 15k Owner mentioned he would like to get 120k but that number is negotiable. He would remaIn the owner and contInue to pay the mortgage. I would propose a base price of 90k and I would put up 15k and manage the project from notice to vacate through sale. Upon completion he would receive base sale price (90k) I would receive my actual repair budget, then we would split the remainder. I’ve left out the little things like who pays utilities, insurance etc.. I’m sure this has been done before, any advice/links to advice would be great. Need to make sure I’m doing this correctly and not exposing either of us to unnecessary risk.