Hello aspirant,
For getting into top colleges like nits, spa delhi, nit trichy, your rank should be in top 500.
The cut off of barch courses is about 50% of total marks and above 70% marks you can get a seat in the finest institutions of India offering B.arch.
Basically, if you want to get any nit your rank should be in top 2.5k or 3k.
Hope it helps.