Came in to design building (6)
I believe the answer is:
cinema
'building' is the definition.
(cinema is a kind of building)
'came in to design' is the wordplay.
'to design' indicates anagramming the letters.
'came'+'in'='camein'
'camein' with letters rearranged gives 'CINEMA'.
(Other definitions for cinema that I've seen before include "place for pictures" , "Film industry" , "Motion pictures" , "Odeon perhaps" , "The flicks" .)