Advice on structuring Deal / Payment

[Account Closed]

Hello BP, I am starting a rehab / flip project on my parents home. It was ran down and they were ready to sell as is. I decided to propose that they "sell it" to me and let me flip it. They agreed to doing this, and we have set a "sell price". 

I'm using quotes because we are not actually going through the process of selling it to me but rather, we agreed on a sell price and at the sale of the property to another party I would receive all additional proceeds over the agreed upon "sell price". 

My Question is two part: 

• Should I have an agreement in writing, if so who would be best to reach out to (CPA, Lawyer, etc)
• How should I structure the payout to me? (Deed, Gift from parents, Invoiced via newly created LLC?)
  • I am looking for an option with the best tax-savings