Extend upwards and cheer loudly (5,3,4)
I believe the answer is:
raise the roof
I'm afraid I can't even guess how this answer relates to the clue.
Can you help me to learn more?
(Other definitions for raise the roof that I've seen before include "builders put in new storey?" , "Make a great commotion" , "cause a massive disturbance?" , "Make a great noise" , "Complain loudly and angrily" .)