Seller holds the note while you flip.

[Cody Campbell]

I'm working on a deal to buy a house. Currently the house is a 3b/2b home with partial basement and detached garage and is on the market for 119k, local comps show same area and same size at around 120-130k. The house is in much needed repair. I'm going in to purchase the house at 50k with 35k in rehab costs, am I'm also offering 20% of the profit after the flip. My question is how do I write up for the seller to hold the note? Should I do 15yr with payments beginning in 90 days? 30yr? It's a hypothetical question but would truly love some feedback. Has anyone done this? Seller hold the note during the flip?