Seller Financing For Developing

[Nick Mokan]

Hi all! Not a first time investor, but first time looking at an opportunity involving  seller financing. 
In short, seller owns a property that I’m looking to develop a new house on. They are open to carrying the note during the course of construction and getting paid when the newly built house is sold. I will be obtaining construction financing as well as doing the development work. 
basic numbers are : PP 1.4M, development 1.5M, ARV 5M.
Of course there is cost of financing, carrying costs, seller fees, state excise taxes in all of this.
How would I structure a deal Like this with a seller to be safe in my investment and to give the seller a pice of mind that they will be paid upon sale? 

Thank you all!