Hi Buddy,

IIT Madras is one of the most prestigious college in india and as you said Admission is through JEE Main -> JEE Advanced -> Josaa Counselling.

For JoSAA counselling 2021 (Documents for IIT Admission)

• Class X Mark Sheet/Certificate or Birth Certificate (for Date-of-Birth)
• Class XII Mark Sheet (Qualifying Examination)
• Crossed Bank Cheque copy / Image of Passbook with bank account details
• Medical Certificate
• Certificate of category (SC/ST/OBC-NCL/GEN-EWS), if applicable
• In case of OBC-NCL/GEN-EWS category, the certificate must be issued on or after April 01, 2021.
• Original Certificate for Persons with Disabilities (PwD),
• OCI/PIO card
• Passport / Citizenship certificate, if applicable
• Category Certificate (SC/ ST/ OBC-NCL/ Gen-EWS

I hope that might help.

Thank You!.