Knowing that, you know that if you want zero of your own money in the deal, you can't spend more than $75,000 total.

And it's only about a quarter of your total build cost.For a quick reference and depending on your finishes you can assume that your build cost will be somewhere between $120 and $200 per SF, not inclusing land, architctual plans, developemnet costs, impact fees, overhead and holding cost. 

The bad news is that this property is in a living trust since his mother passed away, and there's a total of 6 siblings on this trust.

They will typically ask for 15-20 % of the total project costs and at least 6 months of mortgage payments to fund your project.

Totally impressed and would like to get into this type of market in my area.  

So six people in total will be living in the house.

The total replacement cost will be a fixed amount, and once she get's up to $400 the plan is to have it replaced.

The total rents are $2,300, and heat in the winter runs $200/mo, and water runs $100/mo.

I own 2 homes in the DC area and have a total of about 400k equity on one and 100k equity on the other.

Is there an "average" total tax percent I could use across deals to get close before I dig deeper for the actual numbers  or do they vary significantly?