However every lease is different so there may be some structural costs you could have to pay such as a roof replacement, but if it's an absolute NNN then you don't have to worry about it. 

Is the roof toast?

It needed a new roof and windows which scared off other buyers, and both units were significantly under market rent.

Also, I only take care of the inside of the unit so very little issues there, so less expense.My SFR's are different in that I need to have some money to address major issues, like Roof repairs, painting (inside and out), etc. 

I just spent more than twice this amount to put a new roof on my re-hab.

Especially the roof - don't wait for it to fail.

Location: Columbus, OhioLayout: 2 side by side separate units, each 6BR/2BACurrent Use: Airbnb STRI will be inheriting the future bookings through end of April, but will then need to do some work to the roof and then decide if I want to continue with STR or go LTR (very near OSU campus so possibility of student housing). 

Structural repairs, paint, roofs... you name it.

But to summarize these requirements think big ticket items, roof, electrical, and foundation.

For all of them... what are the age of the systems (roof, a/c, pool equipment, water heater etc.