I opt to work round a terrace (5)
I believe the answer is:
patio
'terrace' is the definition.
('patio' can be a synonym of 'terrace')
'i opt to work round a' is the wordplay.
'to work' is an anagram indicator.
'round' is an insertion indicator.
'i'+'opt'='iopt'
'iopt' with letters rearranged gives 'ptio'.
'ptio' enclosing 'a' is 'PATIO'.
(Other definitions for patio that I've seen before include "yard" , "Place to sit" , "Where to put barbecue" , "Paved eating area adjoining house" , "Hard surface" .)