In my area water is required for habitability for sanitary reasons.

You don't want to over improve a brrrr. rough napkin math: 70k purchase price + 46k rehab = 116k all in160k sale price *.92 (8% cc) = 147k147k - 116k = 31k profitSeems like a decent deal if you can sell. 

With a requirement to hold and rent to Section-8 for 5 years upon completion.Much safer loan, much more likely to house these people in safe sanitary conditions (over the long haul).Just my 2 cents.

I would start looking at what type of properties you're going to acquire and where and then start backing into what they might cash flow and cost and where that money is going to come from. 10 year back of the napkin model/ assumptions1 unit at $60k is $18k down payment at 70% LTV and lets just assume it cash flows $100/month no matter what for easy math.

@Ted BarrettIt's not really a rule but a napkin math theory to estimate if an investment is "good" from the twenty teens.

.), the location, depth, and capacity of utilities to service the site - including public utilities (sanitary, storm and water services), franchised utilities (power, gas, cable), capacity of the local streets to accommodate additional traffic from your development...Be sure to find out if there are any specific local ordinances you need to satisfy (possible tree & wetland surveys, together with any necessary tree & landscape or wetland mitigation plans) and whether there are any concerns from municipal departments (e.g. hydrant locations from the fire department, storm inlet and retention requirements, as well as asphalt / concrete road requirements from the engineer), entrance requirements from the road commission (left turn and passing lanes at the site entrance), etc.Once you get past all this you can finally prepare a preliminary site plan and enter the political arena to get preliminary site plan approval, and to address any concessions the board and neighbors want from you to overcome their objections to your development.

But I need to model it out more than just my napkin math.

Here's a simple method: https://www.facebook.com/share/v/L3rQkN4K5teAtk3r/Do this enough times and soon you'll be analyzing properties in your head or on a napkin. 

Napkin math on offers to get a rough idea, then a deep dive when under contract.

Your tax bill is 4x bigger than seller's accurate T12 numbers.To summarize, the seller numbers are really only useful for a very back of the napkin analysis.