Engineer cut iron cost with new building (12)
I believe the answer is:
construction
'building' is the definition.
(I've seen this before)
'engineer cut iron cost with new' is the wordplay.
'engineer' indicates anagramming the letters.
'with' means one lot of letters go next to another.
'new' becomes 'n' (**).
'cut'+'iron'+'cost'='cutironcost'
'cutironcost' anagrammed gives 'constructio'.
'constructio'+'n'='CONSTRUCTION'
(Other definitions for construction that I've seen before include "Act of building" , "Building; interpretation" , "Industry of erecting buildings" , "Process of erecting buildings" .)