Using room that's turned out huge (9)
I believe the answer is:
ginormous
'huge' is the definition.
(I've seen this before)
'using room that's turned out' is the wordplay.
'that's turned out' indicates an anagram.
'using'+'room'='usingroom'
'usingroom' with letters rearranged gives 'GINORMOUS'.
(Other definitions for ginormous that I've seen before include "Big (slang)" , "Huge" , "Titanic" , "jumbo" .)