Structuring the Relationship with Investor and Project Manager

[Jonathan Jenkins]

I work for an investor as his acquisitions specialist and help him find deals. I am a broker, but also operate as his project manager. He has about 25 SFR that he holds for rentals.

For the last property he acquired, he paid me hourly while I managed the rehab (planned, hired, budgeted etc) and then turned the property over to our property manager for him to rent it out.

We are wanting to focus on flipping a few projects and not holding. He is willing to offer me a percentage of the deal/profits but we don't know how to structure it.

My role will be finding the property and acquisitions (here ideally I will be compensated with a commission or finders fee if off market), and then manage the process until it is ready to be sold.

I have read some posts about the project manager taking a % mark up on the cost of the rehab. My issues with these are 1) I want to keep the rehab costs as low as possible as if I was the investor, and do not want to be rewarded for higher costs
2) Soon I will be putting money in projects with him as a partner, and my mindset is analyzing deals that will have the highest return and want to be rewarded or penalized when the project does not work out like planned. 

What would be a reasonable percentage of profits for me running the whole project and just using his money? Profits =resale of property - rehab costs - hold - purchase price