Hi Ansh,

B.Arch. is an Undergraduate course of duration 5 years. if you  want admissions to this course, the most prominent examination is  the JEE-Mains Paper-2. For eligibility, you need to have passed 12th with at least 50% of marks. you can find more information on this page:

https://engineering.careers360.com/articles/jee-main-paper-2-syllabus

You can also answer the NATA examination which is conducted by the COA. it has  a similar eligibility criteria and more information about this examination can be found here:

https://engineering.careers360.com/articles/nata