Itachi perfect Susanoo
Madara perfect Susanoo
Madara perfect Susanoo (chakra stabilized)
I hope that helps guys. Madaras is bigger because he is adept at Susanoo and was known to have one of the most powerful chakras in Narutoverse. The stabilized version is only exclusize to Madara though.
i have extensive knowledge about Susanoo and prolly will explain it all in a thread later but right now i gotta go to class,i can maybe reply there but it wil be hard