Finally sell the building to a brick company (4)
I believe the answer is:
lego
'a brick company' is the definition.
I know nothing about this answer so I cannot judge whether it can be defined by this definition.
'finally sell the building to' is the wordplay.
'finally' indicates one should take the final letters.
The last letters of 'sell the building to' are 'LEGO'.
Can you help me to learn more?
(Other definitions for lego that I've seen before include "Building bricks for children" , "Toy consisting of interlocking plastic bricks" , "constructed without care" , "Toy building blocks" , "Toy construction set" .)