I've thought mostly about getting a place with multiple beds or multiple units and doing rent by the room.  

Biggest suggestion would be to make sure you are flexible, willing to work with multiple housing programs, and hire a good manager if you are not going to self manage the units.

I have one myself that I funded after selling my SF home and once I set up my policy, I took a low, simple interest (5.5% for me) loan that I then used to purchase a 4 unit MF; now I'm using it to fund the renovations.

Purchase a multi unit building, managed by a management company. 

I did fall into the trap of looking outside of Utah, and I still have one of those deals in my portfolio, but the equity position on my units here are substantially better.

I have a property I own with 2 commercial units on it (A Subway restaurant, which I own, and a dance studio).

Plan is to add two additional units to the bottom floor and remodel the upstairs unit. 

I am at a stage where I can make 2 separate units as the lot is zoned multi unit. 

Typically when it comes to housing you'll want to stick to 3-story garden style without elevators and 18-24 units per building.

The potential risk of foundation movement and settling in the neighboring unit is high and they will be looking for compensation for any issues your underpinning job causes.