Policemen try to provide building material (6)
I believe the answer is:
cement
'building material' is the definition.
(cement is a kind of building material)
'policemen try to provide' is the wordplay.
'to provide' says the answer is hidden in the clue.
'CEMENT' is hidden within 'policemen try'.
(Other definitions for cement that I've seen before include "Glue" , "binder" , "It hardens when wetted" , "Join firmly together" , "Firmly establish" .)