Rundfunkbeitrag: Student dorm – How many can register for Radio tax?

I live in a student dormitory in Germany where about 50 people live in the same building. One student has registered and is paying the ARD radio tax (Rundfunkbeitrag) per floor.

How many can regsiter under her name? How does the system works?

Would really appreciate any advice or clarification from anyone who's been in a similar situation. Thanks in advance!