Hi Aqil, NATA exam is not compulsory for B-arch.you have another option called jee-main paper 2.with the help of jee you cat get good college but jee accepted college are less as compared to NATA college. 

NATA paper examines the quality of students through the aptitude test and drawing test.NATA prefer almost every other college.with NATA good score your chances are high to get admission in good college.

thank you