Due Diligence MultiFam New Construction

[Will B.]

I'm thinking about participating into the construction of a multifamily in New York City.  Project is 18 MM.  A group is self-financing 9MM and borrowing the other 9MM.  Apartments will be sold upon completion.  I initially approached it to buy an apartment years before it was to be finished, thinking I could get it at a lower price but discussing it with the owner of the development, the idea of investing my 500K came up.   I could then use my investment+earnings toward the purchase of an apartment or reinvesment in their next project.  This group has done this for years.

 I have done single family flips before, me funding the whole thing from beginning to end. I own and manage a small multi-family but I have never done a deal of this magnitude but would like to graduate to a higher league where I just put up the money and someone else does all the work.

My question is, what is the due diligence one must do on a deal like this?  What are the key questions to ask?  What are the average terms of such a deal?