NATA

Please refer to the link provided below via which you can navigate to the SILICA website. Once there, you will have to provide your contact information and then the coaching institute will provide you course details and fee structure.
Link: http://www.silica.co.in/

(Board score/2)+(Nata score/4), if
it is 80 then you will get a top college.
If 75 then you will get a good college.
If 70, you will get an average college.
If 60, you will get a decent college.
This rule is for general category and candidates belonging to outside state category, for first merit list.
Hope this helps.

Hi,
Please refer to the link provided below for details on admission criteria and eligibility to gain admission into the college of your choice. Your 12th results seem to be fine but your NATA score is low. You will get a more accurate picture if you get in touch with the college admissions bureau. You could also try for admission through management quota.
Link: https://www.shiksha.com/college/sir-j-j-college-of-architecture-mumbai-24830

Yes, you can appear for the NATA exam after completing your HSC.

NATA qualifying examination scores are valid for a period of two years starting from the date the individual appeared for the examinations. Admission into an institute accepting NATA scores is not possible before you have appeared for the exam.

For IIT you must clear JEE Mains and Advance and then AAT.

You can appear for NATA but you can't get admission in architecture course as the eligibility criteria is 12th passed with maths and English for science students.
I hope it will help.

You only need a minimum of 55% in class 12th. Qualifying marks in NATA would be governed by the following rules. You must satisfy all three rules to qualify.
1. At least 25% must be secured in MCQ portion (30 out of 120)
2. At least 25% must be secured in drawing portion (20 out of 80)
3. Overall qualifying marks (out of 200) would be based on post-exam statistics and at the discretion of
the council.