Hi every one  I am brand new, just signed up to bigger pockets today.  I have a unique opportunity with a piece of property I obtained in the booming Uptown Charlotte 3rd ward neighborhood.  I purchased the small house here on a 1/4 acre lot for $172k.  I rolled some money from another property over so currently I have no mortgage but a lien of $66k.  I have gone through the process of splitting the lot in to a flag lot, 2 parcels, and have just finalized architectural plans to build a duplex on each lot, 4 units total.  Each unit is about 2,040 square feet, 3BR/3.5BA, 2 car garage, rooftop patio.  I'm hoping I can team up with a builder that can keep our cost down around $100/sq.ft., which would make building cost about $816,000.  Additional costs, land prep, demo house, permits, etc. puts us in at about $900,000.  These are selling like hot cakes, very low supply and the other new similar townhouses that have hit the market are off within a week or two.  The list price for these units will be $450k/each, total of $1.8M.  
Less some realtor fees this gives us a profit around $850k.  I have put in about $150k of my own money to get us to the point we're at now.  I am now bidding out the project to builders who would fund the project and build it in exchange for a % of the profits or sale price, an equity partner.  What is a fair amount to split this up either on the sale price or as a percentage of profits?  A couple have said they would split the profits with me.  Has any one done a similar deal or if you could point me in the right direction that'd be great! 

Thanks,

-Chris