Build up hotshot to take over French vineyard (6)
I believe the answer is:
accrue
'build up' is the definition.
(I've seen this in another clue)
'hotshot to take over french vineyard' is the wordplay.
'hotshot' becomes 'ace' (synonyms).
'to take over' indicates putting letters inside.
'french vineyard' becomes 'cru' (I've seen this in another clue).
'ace' going around 'cru' is 'ACCRUE'.
(Other definitions for accrue that I've seen before include "Collect" , "Show increasing interest" , "Increase by periodic additions" , "Grow by adding to" , "Be added to, develop" .)