For example, for capex I will look at estimated life expectancy of things like HW heater, A/C, appliances, roof, windows etc.

My other thought was to sell before it needs a new roof. 

Instead of worrying about the label “tornado alley,” focus on the actual property features:How is the roof condition and age?

Those may have similar docs where each side agrees to pay for half the roof when needed or siding, but that gets association shared expenses down to very little, maybe a small shared insurance policy for the full roof as you aren't going to replace half a roof.Small condo associations (2-units) also may lead to more frustrations if there is a dispute on how to maintain something and who to turn to if one side isn't paying or keeping things looking nice. 

Even if bought below market value, one major capital expense—like a roof or water service line—can erase all perceived equity.

Roof 2.

In Maryvale (Phoenix, next door) ( basically the other end of the spectrum,) you'd look at the basics, roof, AC, kitchen, bathroom, floors, door knobs (hardware), switches, lights and you'd change it from antique Mexican flavor to newer antique Mexican flavor, and profit about $60,000 in shorter time.

Avoid early projects with stacked structural, sewer, roof, and electrical hits unless deeply discounted.

Quote from @Sharon Bancroft: I need a loan for a roof.

Depending on the roof age, type of coverage, and deductible amount the 4 plex could be a little high.