With a rank of 18k, it's difficult to be able to get into any NITs or SPA programs for B.Arch. However, you can try other Architecture colleges.

To follow up criteria of various colleges, Visit https://engineering.careers360.com/colleges/list-of-b-arch-colleges-in-india 

Hello aspirant,

For getting into any B. Arch program, one must appear JEE Mains paper-2 or NATA.

Paper-1 marks are not considered for architecture.

Good luck!