We built a single family home version of a 2 bed 1 bath with surface parking at cost with no profit all in with land for 175k in newark ohio, a suburb of columbus ohio. when we push that to 3 units and closer to the city for our build to rent model the numbers go way better. a 30k slab for a single family home is 30k, a 30k slab for a triplex is 10k a door. we designed a 2 bed 1 bath design at 668 sq ft and it's very good layout even I would live there, but I would never build anything that small again. there's no economies of scale. you need density and shared lines, resources, shared roof shared slab, shared windows, etc the cost goes way down.

I saw a notice on the door from the city and I tried to get some info on the owner but it looks like an investment company has owned it for several years but no one has been in there.

houston is probably similar pricing to Columbus Ohio but way worse zoning laws. we take 20% on top as a GC and a guaranteed fee agreement. our contracted new construction projects recently:Single family new build spec home: 1513 square feet with 3 beds 2.5 baths 1 car attached $275000 approx $182 a square foot if calculated using heated square feet which means our cost is $145 a square foot. 3 unit / triplex new construction: 2008 square feet 2 bedrooms 1 bath per unit or total 6 bedrooms 3 bathrooms with 3 off street parking spaces. contracted build cost $395,000. no garage on this and better economies of scale with shared roof, slab, etc. $192 a square foot hard cost with our cost running approximately $157 a square foot. 

The 3 apt + 2 Commercial Garages is a unique property.

Initial and only door, thus far.

The properties are often flawed and no well-suited for a family to live there long term (lot's of bedrooms, but tiny living room, no yard, no garage etc), that's why they sold for a discount an get used as STR.

I don't remember exactly, but its on top of my 2-car garage, so 20 ft by 22 ft maybe?

@Von Wilson you could ask the developer next door to partner with you and have them build on your property.  

He installed doors on the living room to turn it into an extra bedroom.

While the math per door is roughly the same, my thought is that I will have more doors still rented while I renovate one, and the overall costs for maintenance is roughly the same.