Check the condition of the roof, siding, windows, pavement, lawn, deck, porch, driveway, garage door.....walls, floors, light fixtures, switches, outlets, furnace, AC, pipes, stairs...

Quality of the Roof.  

The exterior was in bad enough shape that the siding was roof shingles that didn't even overlap, they just butted them up against each other, so they were peeling off. 

But what I thought they said is to figure out the cash flow and then divide it by two because history has tended to show that unexpected expenses (new water heater in yr 1, roof repair yr 2, etc) tend to eat up about half of your earned cash flow.  

They don't take care of themselves and when the toilet plugs up or the AC breaks or the roof leaks the PM will not be out there when the tenant starts screaming at you over the phone that they will not pay the rent until you get there at midnight on Sunday to fix the problem.

Exterior paint and roofing would be the largest. 

Roof and masonry work.The building is probably worth, 135-150k depending on the extent of repairs done to it.

And we have found water leaks and unauthorized swimming pools doing it this way too.

I have given investors commercial roofing advice on BP for years. 

They also have various home improvements (replacement windows, repairs to rotted truss in roof, bracing, new decking and shingles in the area among other things) that have no permits.