Partner in new construction deal contract

[Aurian Saidi]

So I was planning on selling my single family house but a builder approached me with this offer. They said it will take 15 months to build a new house on the property and the building cost will be $635k which they will pay for and then we would will split 50/50 the estimated profit of $800k. I would appreciate some advice on the protection this contract would give me and wordage I should change. Thank you