Read the phrase. the windows of the buildings which is the correct way to rewrite this phrase? the building’s windows the buildings’s windows the buildings windows the buildings’ windows

Greetings!

The noun (buildings) is a possessive noun, meaning that it has a relationship of owning the other noun (windows). However, the possessive noun in this case is plural (ends with s) and is thus treated differently than a singular possessive noun: 

Singular: 
Building's Windows

Plural: 
Buildings' Windows 

In this scenario, since possessive noun end in s/is plural, we don't add the s.
The answer would therefore be the last option, "buildings' windows" 

Hope this helps!
-Benjamin