My assumptions based off research is I will be able to deduct 1/2 of all allowable expenses based off the ADU square footage (My understanding of that list below)  1/2 Mortgage Interest (Not principle) 1/2 Utilities 1/2 Property Taxes 1/2 Insurance (assuming I don't have separate ADU insurance)  1/2 general house maintenance (depending on the issue and if it's related to the ADU)  1/2 Depreciation (Home value, not land divided by 27.5)  KEY QUESTION: If my mortgage (PITI) is $5400, and all of those ADU deductions equal $3800 monthly, and my ADU income is $1800 monthly, am I allowed to pay the difference in "deductions" from my real estate business income? 

@Tamera Means depending on sq footage and quality of finishes you're looking at 100-150k all in.

I found this odd, so I decided to call Cobb County and they advised that a basement can only be rented by one adult with some kind of square footage per person limitation, and I could not wall off the basement door.

Only a small amount of footage (I believe 150’) can be added for ingress/egress purposes only.  

If that is not possible I am hoping to build the maximum number of bedrooms for the minimum square footage of 1800. 

And you know you lose a whole lot of square footage because of the roof angle, right?

It had a lot of square footage and already had some cool historic touches.

To help guesstimate numbers I would be interested to know square footage, number of bed/baths, how much remodeling is needed, info about the outdoor space, and where the property is located.

You can house hack a mixed-use commercial property with an owner-occupied loan (and FHA) if the residential square footage is 51% or more.

Montgomery County has specific requirements on square footage, parking, and permits for ADUs, so you'd want to check those out before making any moves on a basement conversion.If you're just renting out rooms in Montgomery County, you're good to go!