Rehab a 70 year old apartment building

[Doug Wang]

I am from Los Angeles and found an apartment building in Fresno.  Escrow closes in two weeks.  The building was build in the 40th and maintained most of its original beauties: red tile roof which is leaking and the roof support shows signs of giving up, original electrical system without ground wires, rotted floor joist, original metal windows.

There are 8 units in the apartment and I paid about $37k per unit.  My renovation budget is about  $13k per unit, which will not cover all problems.  

My question is where I should spend my money?

New roof, rewire, HVAC and then floor and windows?