They showed her a permit from the city (just got at the same time with the roof replacement permit), which allowed to install a front door for the back unit.

But I think I can just as well play the role of business owner, since I think I have more value to offer there.The business would require about 2-4 acres of property to build an air-conditioned warehouse-like structure with customer parking.  

Initial thoughts are doing the opposite and live in the main house while renting the apartment either log term or VRBO/Air BnB but the apartment unit is not permitted per the listing agent.This is in Central California.

As for taxes, I carry over lodging, bed, and the soon-to-be sales tax in my town, to my customers.

FHA requires inspections, seller-paid repairs to code, everything must have been perfectly permitted).

I am an active GC and am currently performing a variety of services to a range of customers.

Professional real estate investors and property managers always conduct a custom "rent survey". 

Brian Ray PM when time permits.

@Ritch Bonisa thank you for the input, that's true I didnt put the codes into consideration, the house been empty for 5 plus years, who knows what's not in code, plus applying permit time around the area is a pain also, it could delay rehab time and increase holding costs. 

There's a guy in contract for a property contingent on the permits being approved.