On regular roof, statue is well-built (6)
I believe the answer is:
robust
'well-built' is the definition.
(I've seen this before)
'on regular roof statue' is the wordplay.
'on' is a charade indicator (letters next to each other).
'regular' means one should take alternating letters.
'statue' becomes 'bust' (I have seen 'Small statue ' mean 'bust' so perhaps 'statue' could also mean 'bust').
The alternating letters of 'roof' are 'ro'.
'ro' put next to 'bust' is 'ROBUST'.
'is' is the link.
(Other definitions for robust that I've seen before include "No-nonsense" , "Sturdy and hardy" , "Study and durable" , "Hardy and vigorous" , "Full and rich (wine)" .)