Which entrance should I write to pursue B.Arch from IIT? Which coaching centre should I join to achieve my aim?

It is just great that you have thought to study B.Arch at IIT. You should appear for JEE main paper 2 (B.Arch). Almost all the coaching centers are good. I don't want to mention any coaching center names. If you want to get into any best institute then refer those which produced the toppers in JEE