People with 5+ houses how do you save for expenses and repairs?

[Evan Smith]

I Ill have 6 houses by the end of this summer which range from triplexes to quads. Overall ill have roughly 20 units. Im curious how people in my situation save for expenses. I used to save per house and just keep it in my bank account but at this point im thinking about just keeping a lump sum x amount and if it goes down I just replenish it to a certain point. 

With my monthly rent at this point I could pay for a roof or something else if it goes wrong one month. Obviously if I had a ton of huge stuff hit me at once I would have to do it over a few months, but im thinking it might be a waste to continue saving instead of just buying more properties. Curious to see what others here do.