building vs assembly

building and assembly both are nouns.

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

As nouns, assembly is a hyponym of building; that is, assembly is a word with a more specific, narrower meaning than building:

building (noun)	assembly (noun)
the act of constructing something	the social act of assembling
the commercial activity involved in repairing old structures or constructing new ones	the act of constructing something (as a piece of machinery)
a structure that has a roof and walls and stands more or less permanently in one place	a group of machine parts that fit together to form a self-contained unit
the occupants of a building	a public facility to meet for open discussion
	a unit consisting of components that have been fitted together
	a group of persons who are gathered together for a common purpose