Roll up a hill (4)
I believe the answer is:
rota
'roll' is the definition.
(I know that rota is a type of roll)
'up a hill' is the wordplay.
'up' says the letters should be written backwards (in down clue: letters go upwards).
'hill' becomes 'tor' (tor is a kind of hill).
'a'+'tor'='ator'
'ator' reversed gives 'ROTA'.
(Other definitions for rota that I've seen before include "Roll call or roster" , "Working times list" , "List of people to do job in turns" , "List assigning turns of duty" , "Work roster" .)