Depends on:- Location- Types of contractors you use- How the project is managed (GC or Self)- Level of Finishes- Time of Year- Permit and Impact Fees- Your Negotiating SkillsLooks like you're in Atlanta -- you're likely somewhere between $80/sf and $150/sf, depending on the things above. 

Bit of background - The property is in a commercial area and I believe at one point in time was a hair salon.Given this is my first rental and my inexperience I reached out to a couple contractors and one of them told me to start at the permitting and zoning office.

NJ uses the same codes across every town and the paper work is pretty much the same for permits etc.

Ironically, it actually discouraged me from building a permitted ADU and opting for a nonpermitted basement ADU for au-pair quarters and later on airbnb (STR not allowed for permitted ADUs/duplexes etc) which seems to be a better return on investment vs. long term renter if living close-in. 

In my city not only do you need a permit but every household within a certain distance of your building has to sign off on it.  

Lastly, you could study permit data to get a better idea of how the relationship between supply and demand is trending in your target market. 

Both inspection reports called out a long list of repairs, although the previous inspection had more issues that I addressed before the new buyer's inspection.Buyer's claim: buyer send me the attached letter claiming that he bought the house because he thought it was renovated well and now he has to spend money on renovations and repairing damages resulting from the unpermitted workMy claim:The buyer had never asked for permits and neither me or my realtor ever claimed permits were pulled for any work. 

How much for permits and how long. 

Not only that but you need to know the cost of material and labor, in that specific area, plus regulations, permits, SID's, and something else will inevitably pop up.I would at minimum pay for a contractor to walk through it without you there.

Would be interested to hear what area of town this was in A client of mine has found success putting her duplex on Airbnb for a minimum of 30 days allowing her to negate the required STR permit.