Before I went through the process of hiring a contractor to evaluate and price out, acquire drawings and talk with the building department.

Never give a down payment (may be a just small commencement fee if the builder signs a triparty agreement with the bank) the builder will get draws from you and the bank together. 

But if I live downstairs how are the house expenses divided?  

The large backyard can be divided and I can build another single family dwelling on it which is allowable by local zoning laws.  

Its a large canvas, up to you what you want to draw so to speak.

I know it will be good to draw up responsibilities with a lawyer and a contract between us.

In each case, the clients invested in areas where the tenants were primarily medical or law students in the city/urban area; the square footage is small which contains rehab costs and the draw is location and amenities.

They're going to draw a range of people.

What draws your interest to that one zip code?

However you can charge a higher amount and divide that over how many months they will be paying you.