Block put on new farm building (4)
I believe the answer is:
barn
'farm building' is the definition.
(barn is a kind of farm building)
'block put on new' is the wordplay.
'block' becomes 'bar' (bar is a kind of block**).
'put on' is a charade indicator (letters next to each other).
'new' becomes 'n'.
'bar'+'n'='BARN'
(Other definitions for barn that I've seen before include "Farm storage building" , "spacious accommodation" , "Large outhouse" , "Large farm outbuilding" , "Large farm building" .)