Well, your B.arch seat percentile will depend on the college you are desiring to taking admission into.

It will be easier for me to help you out with the required percentile, if you can mention the name of the college or your desired location.

You can check the JEE main paper 2 cut off 2020 and college predictor from this website.

https://engineering.careers360.com/articles/jee-main-cutoff-for-b-arch-b-planning

Feel free to comment your queries.