Mixed use Developer cost?

[Jim Perin]

HI All!  Found BP a week ago and has been a great tool to find out answers to my questions but can not find one of them.  This question is just very general but will lead to a MUCH bigger conversation later so here goes.

I am looking to develop my property.  I have 20K sq ft in a VERY desirable city in NH.  I wish to but up a 5 story mixed use building, 1st. floor retail/restaurant 2nd to 5th apartments.  There will also have to be some underground parking.  I estimate the cost for entire including soft fees will be about $20M.  

What would the fee be for the development company?  This company would have to get financing, have the means to construct the building, ect.  After the building is completed they would just hand over the keys to me.  I know there is more to this but I just need to get an idea of how much this would cost.  Thank you  Jim