Fence built by mate in front of gazebo (6)
I believe the answer is:
paling
'fence' is the definition.
(I know that paling is a type of fence)
'mate in front of gazebo' is the wordplay.
'mate' becomes 'pal' (I've seen this in another clue).
'front of' indicates taking the first letters (the letter at the front of the word).
The first letter of 'gazebo' is 'g'.
'pal'+'in'+'g'='PALING'
'built by' acts as a link.
(Other definitions for paling that I've seen before include "is becoming whiter" , "Fence made of stakes" , "Barrier of stakes" , "Fence post - turning white" .)