Investing with family - get a promissory note?

[Kyle Morse]

Hi, 

I'm a relatively new investor - I currently own one duplex that's fully rented, and have one completed flip property on the market to hopefully sell soon.

My next step is partnering with a family member - an uncle - who has expressed an interest in providing me with financing to help me scale my business. To start, we would partner on flipping a single family home.

My question is - what documents should I set up with this family member? 
A promissory note? An LLC? Anything in particular to make sure we're all set up to buy a property?

He would be providing 90-100% of the financing, I would be coordinating the rehab process.

Thank you for any advice you're willing to provide.