Yes, your sentence is possible. (It's certainly grammatical.)
However, the common interpretation of the first sentence is not what you think it is (and it's not because of the possessive).
I want to buy a building's corner.
I've never heard of people buying just the corner of a building before. So, if I heard this I would interpret it differently:
I want to buy the corner of the block on which a building stands.
In this interpretation, the building's corner is referring to something else—although still something that's associated with it.
To make it explicitly clear that it's the physical component of the building, you could say:
I don't want to buy the entire building. I just want to buy one of its corners.
I want to buy the building's southwest corner and all of the offices therein.
Again, the possessive is fine—it's the subject being referenced that needs clarification.
But if you use a different particular sentence, this type of confusion won't exist—and the regular possessive can easily be used:
The building's windows were broken.
I want to paint the building's hallway walls.
The storm flooded the building's lobby.