Get garage rebuilt for a sum (9)
I believe the answer is:
aggregate
'a sum' is the definition.
(aggregate is a kind of sum)
'get garage rebuilt' is the wordplay.
'rebuilt' indicates an anagram.
'get'+'garage'='getgarage'
'getgarage' with letters rearranged gives 'AGGREGATE'.
'for' is the link.
(Other definitions for aggregate that I've seen before include "A whole formed by combining several elements" , "Accumulate into total" , "Sum of many heterogenous things taken together" , "Material to make concrete, mortar, or plaster" , "All - broken stone put in cement" .)