Hello Aakriti, Greetings!

If you want to go for B.Arch in NITs, then you need to give only Paper-2, in JEE Main.

For B.Arch in IITs , you have to give both JEE Main and Advance exam and AAT exam(Architecture Aptitude Test).

You can appear for AAT, only if, you are able to secure a rank in the common exam of JEE Advanced. Then, based on your rank, you will be allotted a seat, through centralized counselling process.

Thank you, best of luck.