Architect Charlie enters, generating endless rubbish (10)
I believe the answer is:
mackintosh
'architect' is the definition.
(architect Charles Rennie Mackintosh)
'charlie enters generating endless rubbish' is the wordplay.
'charlie' becomes 'c' (phonetic alphabet: alpha, bravo, charlie etc.).
'enters' means one lot of letters goes inside another.
'generating' becomes 'making'.
'endless' means to remove the last letter.
'rubbish' becomes 'tosh' (both can mean nonsense).
'making' with its last letter removed is 'makin'.
'c' placed into 'makin' is 'mackin'.
'mackin'+'tosh'='MACKINTOSH'
(Other definitions for mackintosh that I've seen before include "Weather defence" , "providing protection from the elements" , "waterproof layer" , "Architect" , "Garment" .)