annex vs building

annex and building both are nouns.

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

annex (noun)	building (noun)
an addition that extends a main building	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

annex (verb)	building (verb)
add an extra part to
take (territory) as if by conquest