Common wall/roof

[Ben Nahir]

I am new to REI but looking to purchase my first investment property. It is a town home on my street, no HOA, relatively new (1999), and decently sized for the neighborhood (bigger than my current residence). I'd like to find out more information on common wall agreements and what they cover.

The neighboring tenant owns his half of the duplex, has lived there for at least 4 years, and the exterior of the entire structure appears sound and in good condition. The architecture of the building is such that each town home has one section of roof to itself and one section of roof that is shared (looks like a U). Although everything is in good condition now, it is easy to imagine a scenario in which one part of the shared roof is damaged to the point of needing replacement. Would a common wall agreement cover this and in general, how are the expenses divided? Is there anything I can do to protect myself against recklessness from the neighbor? Does anyone have an general thoughts or comments about purchasing and renting one half of a duplex?