Such evidence as it is that there’s building going on? (8)
I believe the answer is:
concrete
'as it is that there's building going on?' is the definition.
The definition and answer can be both substances as well as being singular nouns.
Perhaps there's a link between them I don't understand?
'such evidence' is the wordplay.
I cannot quite understand how this works, but
'evidence' could be 'con' (con is a kind of evidence) and 'con' is present in the answer.
The remaining letters 'crete' is a valid word which might be clued in a way I don't understand.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for concrete that I've seen before include "Unsightly building material" , "Specific - building material" , "Not abstract or imaginary" , "Substantial, real" , "Real; building material" .)