Leaves fifty out on the roof (5)
I believe the answer is:
eaves
'the roof' is the definition.
(thesaurus)
'leaves fifty out' is the wordplay.
'fifty' becomes 'L' (Roman numeral).
'out' indicates named letters should be taken away.
'leaves' with 'l' taken away is 'EAVES'.
'on' is the link.
(Other definitions for eaves that I've seen before include "Overhanging part of roof" , "parts of housetops" , "Projecting edge of a roof" , "what might constitute a hangover?" , "Overhanging roof edges" .)