5 Unit Value Add Running Numbers

[Garreton Smith]

Hi BP Family, 

I hope everyone is staying safe and is in good health.

 I'm looking to acquire a 5 unit property. Three units are vacant 2 are rented. All units need full cosmetic rehab and rents are below market. The owner won't budge on the purchase price. In your experience what's the best method to run numbers to make sure this is indeed a good deal? I know what the potential rents could be once rehabbed. I also have a good idea of what each unit will cost to renovate. I would be looking to rehab, raise rents and refi out a short term loan to a 30 year. What are the right numbers to run for commercial spaces? 

Thanks for your help in advance, 

Garreton Smith