Their city told them that if the shed sits on the ground, on a poured concrete slab, then it counts towards the square footage for the property tax. 

I started off with bandit signs and I've been getting a few phone calls here an there, but nothing concrete.

@Conrad FehFirst off, congratulations on taking a first concrete step.

 $800/month seems high for a one bedroom apartment in an ugly concrete block box in a challenging Atlanta neighborhood, even if newly renovated.  

I am a numbers guy and while I do LOVE real estate and I love the properties I currently own, I purchase on numbers first, location second, and building type third (I live in Florida concrete block is MUCH more enviable when termites are your state's bug).

Here's what I gleaned as a summary of hardening tips for reducing turnover/maintenance costs:panasonic bath fans with timers in bathrooms4 coats of poly on wood floorsdouble door stopstile floors, showers vs surroundssingle lever shower valve vs. doublereplace toilets with steel parts/mechanicals whenever it starts to runKwikset smart keys (some debate over efficacy)door stoppers on all hingesremove pop-up drains and replace with commercial drains2' drain lines from sinks with an accessible clean outbuy a key cutter - maker for $50 on craigslistGranite tile counters - need a diamond polisher and tile sawUsed Fixed vs. friction shower rodsKeyed deadbolt and passage knob on outside doors to prevent accidental lockout5/8' fire core drywall - can't put a fist thru it and its fire-resistant1/4" board to back up towel rodspolyurethane cabinets under sink to pre seal and drain water to the floor2x4 base under cabinets to prevent particle board cabinets from failing where they meet the floorVinyl scrap under sink and up the back wallBest of luck!

A concrete divider may solve your discrepancy.

What I really like is the owner has just installed new water heaters, new AC, new windows, new concrete parking lot adding 7 offstreet parking (in addition to the attached 2x 2 car garages), and “newer” breaker box and furnaces.

We also have a good friend who owns a concrete company that we could incorporate into our business if need be. 

So before I have concrete poured, I am wanting suggestions from more experienced landlords who have worked through these issues.