Hard worker assembling good part of roof (7)
I believe the answer is:
grafter
'hard worker' is the definition.
(I've seen this before)
'assembling good part of roof' is the wordplay.
I cannot quite understand how this works, but
'good' could be 'g' (abbreviation) and 'g' is found within the answer.
'part' could be 'aft' (I have seen 'Rear part ' mean 'aft' so perhaps 'part' could also mean 'aft') and 'aft' is present in the answer.
This explanation may well be incorrect...
Can you help me to learn more?
(Other definitions for grafter that I've seen before include "Hard worker - corrupt operator" , "One who works hard" .)