Builder's coat put on, hold buttons up (8)
I believe the answer is:
cladding
'builder's coat' is the definition.
'put on hold buttons up' is the wordplay.
'put on' becomes 'add' (I've seen this before).
'hold' becomes 'cling' (I've seen this before).
'buttons up' indicates putting letters inside.
'add' put within 'cling' is 'CLADDING'.
(Other definitions for cladding that I've seen before include "Outside wall covering" , "protective coat" , "protection" , "protective material" , "Protective covering on a building" .)