Masons may roll it up to reveal support (7,3)
I believe the answer is:
trouser leg
'masons may roll it up' is the definition.
I can't judge whether this definition defines the answer.
'reveal support' is the wordplay.
'reveal' becomes 'trouser' (I can't justify this - if you can you should give a lot more credence to this answer).
'support' becomes 'leg' (leg is a kind of support).
'trouser'+'leg'='TROUSER LEG'
'to' acts as a link.
(Other definitions for trouser leg that I've seen before include "One of two on American's pants?" , "part of pants" .)