agreement with passive investor

[Emily Bo]

My husband and I now own two duplex's. We want to buy one more multi-family this year. My sister has some money and says she wants to be a passive investor. My husband and I would do everything, she would just give us the money. I have no clue how to how to write this agreement and what options are as far as how she and I should benefit. Do we just agree that she is my bank and loans me the money at 7-8% interest? Or is there a way where she gets a percent of the net income? Pros/Cons? I've never seen even an example of this type of agreement since we are kind of new, so I'm asking for help :) 

Respectfully, please don't comment to tell me not to do business with family, I get the risk. But, i'd love some insight on writing the agreement so that it is worth it for me as well as her (more for me since I'm doing all the work LOL). Have you successfully done these types of deals, and what were the specific numbers? I really appreciate the input! Thanks in advance!