Roofing expert in row about line (5)
I believe the answer is:
tiler
'roofing expert' is the definition.
(I've seen this in another clue)
'row about line' is the wordplay.
'row' becomes 'tier' (a tier is a row of things).
'about' is an insertion indicator.
'line' becomes 'l' (used when specifying particular lines from a poem).
'tier' enclosing 'l' is 'TILER'.
'in' acts as a link.
(Other definitions for tiler that I've seen before include "Workman who fixes glazed rectangles in bathrooms" , "Roof-worker" , "Craftsman" , "Roof worker" , "Relit for tradesman" .)