These are located in Oklahoma so there is potential for occasional temps in single digits.

This is to say that my 4 year investment yielded net 224K, approx. 56k per year...I did a lot of improvement works on the house: new floors on two of the three floors, tore down a wall down, completely rehabbed the basement, added a bathroom, put in a new kitchen, replaced some appliances and many other cosmetic jobs which were costly but I did myself with the help of my father and the occasional local handyman.

Not sure if you have done or plan to do any occasional interior inspections ( with notice ) or if that is written into your lease .. but something to consider .

Piri Musufayaf, here are occasional meet-ups in Tulsa, for investors.

New flooring, paint, bright lights, some landscaping, occasionally new appliance or two.

Large land plots are selling quickly and for good money.Then I occasionally run across houses with large land plots, which are going for less than the value of the land alone. 

If you come east, you can still find houses - even duplexes and the occasional triplex or {even} quadriplex - for under 100K.  ;-)... of course, you will need to re-invest 10K - 50K in many such properties.

Some condo properties rent weekly to which in my opinion is a lot of hassle, maintenance due to high traffic, and attract some not so good renters occasionally; and with high management fees too.

Until an 'investor' reaches critical mass (escape velocity) in number of units turning enough profit that even the occasional catastrophe won't  change their life style, it's got to be keep your head in the game and all hands on deck.It's all fun until it's not.  

Also as time went by the syndicator became more elusive and occasionally gave me timelines that never materialized.