Build and demolish, we're told (5)
I believe the answer is:
raise
'build' is the definition.
(raising is a kind of building)
'demolish we're told' is the wordplay.
'demolish' becomes 'raze' (I've seen this before).
'we're told' shows a homophone (sound like).
'raze' sounds like 'RAISE'.
'and' is the link.
(Other definitions for raise that I've seen before include "Call up" , "Breed" , "Amplify" , "Gather" , "Heighten" .)