I have shelves of books in my house from a wide variety of authors from Robert Kiyosaki and Robert Allen to Black and Decker's Book of Basic Wiring. 

I think there is a pretty wide range of new construction per foot prices.

I'd say pricing going to be 70-150k range per door... wide range but again we're talking a big area here..

After we have looked at them from many different angles we then reconcile these to arrive at a price or rent. 

Here's the question: Is it a red flag if you find a city that has many multi-family listings that seem profitable, but has A LOT of listings city wide?

The reality is that it will take a lot of work and effort to be successful and he should go in with eyes wide open.Too many people see the 65-year-old REALTOR driving a brand new Mercedes and assume it must be easy.

In terms of rehab costs, they vary widely and you may end up needing much more than $20K. 

Going long distance is quite tricky as you are open to wide array of zip codes to choose from.

Definitely shop around - the variation in cost premiums is wide. 

But there isn't a lot of calculation involved, other than figuring out what your payments would be on different principal amounts, and any widely available online mortgage calculator can do this for you in two seconds.