What Happens if Marijuana FOund in of the APT rooms...

I 'm a college student, Never done any drug in my life, but i m living in a apt where roomates are assined by the landlord (student housing) and we have individual leases for each of our rooms, If drugs found in one room can anybody be charged other than the person responsible for this room, There is no drugs in any common area, and i doubt there is anywhere else because everybody said no for drugs in the apt. But what if somebody have it without our knowldge...

They could only charge the person to whom the room is leased. Common areas are up for grabs....thet would most likely see where the drugs were ie. next to a snowboarders magazine and realize only one person has a snowboard....this would lead to that person.
A common are like a trash can is un-chargable if there are no prints,or leading evidence.