What is a proper noun for building?

A proper noun for a building would be the specific name of that building. Here are some examples:

* The Empire State Building

* The Eiffel Tower

* The White House

* The Louvre Museum

* Buckingham Palace

These names are unique to those specific buildings and are always capitalized.

If you're looking for a general term for a building, you would use a common noun like "building," "structure," or "house."