Roofer may be working here as an act of generosity (2,3,5)
I believe the answer is:
on the house
'as an act of generosity' is the definition.
(something given on the house is free)
'roofer may be working here' is the wordplay.
I cannot really see how this works, but
'working' could be 'on' (on can mean working or activated) and 'on' is found in the answer.
The remaining letters 'thehouse' is a valid word which might be clued in a way I don't understand.
This explanation may well be incorrect...
(Other definitions for on the house that I've seen before include "Roof tiles so" , "Free" , "for no money" , "With the management's compliments" , "No charge" .)