Create more headroom and cheer wildly (5,3,4)
I believe the answer is:
raise the roof
'cheer wildly' is the definition.
I don't know anything about this answer so I cannot tell whether this works.
'create more headroom' is the wordplay.
'create' becomes 'raise' (raising is a kind of creating).
'more headroom' becomes 'theroof' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'raise'+'theroof'='RAISE THE ROOF'
'and' is the link.
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 merry!" , "Extend the house" , "give a fantastic reception" , "Make tremendous commotion" .)