No builder's storeyed construction should be by river (9)
I believe the answer is:
destroyer
'no builder's' is the definition.
(someone who does the opposite of building)
'storeyed construction should be by river' is the wordplay.
'construction' indicates anagramming the letters (answer constructed from certain letters).
'should be by' is a charade indicator (letters next to each other).
'river' becomes 'r'.
'storeyed' anagrammed gives 'destroye'.
'destroye'+'r'='DESTROYER'
(Other definitions for destroyer that I've seen before include "Ravager" , "HMS" , "breaker?" , "Siva?" , "Saboteur" .)