The incident was reported from Begumpur area in Rohini on the intervening night of August 10 and 11.
The condition of the woman is critical and she is yet to record her statement with police.
The woman had gone out with her friend, her boyfriend and the 22-year-old accused.
While returning, the accused offered to drop the victim home and said he would get his car from his house.
Her friend and her boyfriend proceeded in an autorickshaw from Rama Vihar. Soon after, they saw people running in one direction, and learnt that a man was seen running away from a building after throwing the woman from the fourth floor, police said.
By the time the police reached the spot, the woman had been taken to the hospital.
It is suspected that the accused forced himself on the woman and when she resisted, he pushed her off. She was found lying in a semi-nude condition.
Her family alleged that there was another man who was also present there but so far, police have only nabbed one accused.