Obstruct new agricultural building (4)
I believe the answer is:
barn
'agricultural building' is the definition.
(I've seen this in another clue)
'obstruct new' is the wordplay.
'obstruct' becomes 'bar' (barring is a kind of obstructing).
'new' becomes 'n' (common abbreviation eg NT for New Testament).
'bar'+'n'='BARN'
(Other definitions for barn that I've seen before include "Bran stored in farm shed" , "Large shed" , "Farm storehouse" , "Large farm outbuilding" , "Farm building for storing hay or grain" .)