office building vs building

office building and building both are nouns.

Word	Noun	Adjective	Verb	Adverb
office building	Yes	No	No	No
building	Yes	No	No	No

As nouns, building is a hypernym of office building; that is, building is a word with a broader meaning than office building:

office building: a building containing offices where work is done
building: a structure that has a roof and walls and stands more or less permanently in one place

Other hypernyms of office building include edifice.

office building (noun)	building (noun)
a building containing offices where work is done	the act of constructing something
	the commercial activity involved in repairing old structures or constructing new ones
	a structure that has a roof and walls and stands more or less permanently in one place
	the occupants of a building