Sexy man, one with ordinary apartment (6)
I believe the answer is:
'apartment' is the definition.
(I know that studio is a type of apartment)
'sexy man one with ordinary' is the wordplay.
'sexy man' becomes 'stud' (stud can mean an attractive man).
'one' becomes 'i' (Roman numeral).
'with' is a charade indicator (letters next to each other).
'ordinary' becomes 'O' (abbreviation eg in O-Level, Ordinary Level).
(Other definitions for studio that I've seen before include "Film company - artist's atelier" , "Type of apartment without a separate bedroom" , "In which to make a film or programme" , "Artist's workroom - film company" , "Workplace for the practice of art" .)