Running the numbers

[Dwight Jackson II]

I'm a total n00b.  Im, currently looking at a 20 unit building.  I want to reduce the number of units to about 12-15 (the building will also be my primary residence and I plan to be the property manager.  I want to have traditional tenants and use some units as Air Band B apartments. The building cost 15k (I'm sure I could get it for less...its been on the market for a long time (probably a bad sign hahaha), it s in a bad neighborhood, and is a total rehab (roof missing...etc).  My question is, how do i run the numbers on a property like this?   How do you estimate renovation?  Pay a contractor?  and the other metrics needed to see if this is a good deal or not.  I forgot to mention one other tidbit ...I'm an expat currently living outside of the US.