Place no longer functions, decorate building on high street? (4,6)
I believe the answer is:
post office
'building on high street?' is the definition.
(many high streets have a post office)
'place no longer functions decorate' is the wordplay.
'place' becomes 'post' (post is a kind of place).
'no longer functions' becomes 'off' (switched off).
'decorate' becomes 'ice' (to ice a cake is to decorate it).
'post'+'off'+'ice'='POST-OFFICE'
(Other definitions for post office that I've seen before include "Letter delivery service" , "organisation to facilitate communication" , "public building" .)