Top copy and ten more required (4)
I believe the answer is:
apex
'top' is the definition.
(apex is a top or peak)
'copy and ten more required' is the wordplay.
'copy' becomes 'ape' (ape can mean to copy or imitate).
'and' says to put letters next to each other.
'ten' becomes 'X' (Roman numeral).
'more' is a charade indicator (letters next to each other) (some letters added to the previous ones).
'required' means one lot of letters go next to another.
'ape'+'x'='APEX'
(Other definitions for apex that I've seen before include "Summit - pinnacle" , "Culmination" , "Pointed top" , "climax" , "Summit or peak" .)