Man soon set to become a builder (10)
I believe the answer is:
stonemason
'a builder' is the definition.
(I know that stonemason is a type of builder)
'man soon set to become' is the wordplay.
'to become' is an anagram indicator.
'man'+'soon'+'set'='mansoonset'
'mansoonset' with letters rearranged gives 'STONEMASON'.
(Other definitions for stonemason that I've seen before include "Person skilled in preparing rock for building etc" , "One working with, eg, granite" , "Artisan builder" , "Construction worker" , "Chiseller" .)