Private money - contracts/notes

[Ronald Fontenot Jr]

I have spoken to a few people who may be interested in lending me money to help in building my portfolio. I'll be starting with some flips to build cash reserves. 

I understand that a promissory note can be used to secure their investment with me. Is there any other contract or lein necessary or recommended to aid in making my potential investors comfortable lending to me? I want to appear and be a professional as possible. Any advice is appreciated!