Except for IITs other Institutes offers admission based on JEE Main paper2 Marks such as NITs and other participating Institutes, Just do well in JEE Main paper2 and get a seat, While for Architecture courses in IITs You first need to clear JEE Main Paper1 and then JEE Advanced and after that You will appear for Architecture aptitude test once You clear it You will be able to get admission into IIT for B Arch.