After a really keen observation as to how Susano'o forms for the individual uchiha, I came to know about 2 things:
1) The color of the susano'o varies on the amount of hate/love of the user. Like Itachi, his susano'o is red-orange symbolizing happiness(or something, lol) whilst Sasuke's is dark purple symbolizing hate.
2)The weapons initially formed by susano'o are the weapons the user of susano'o first came in contact with in his entire life. Like Madara, the first probable weapon he came in contact with was a katana or sword, Itachi being with Kunai(the magatama rings) and Sasuke the bow and arrow.