Look around your room and see what you can do to get the most space available for a cage on the floor or on a table. You should have at least 56" in length. The length can be made any way that you can. You can have 40" straight then if there is an angle in your room you can make the remainder 16" around the angle. I hope you understand that. Move things around first if you can and which would be the best solution for you. Once you know what you can do then you can work from there.
Just one other thing. Since you stated that you have a number of roommates, please take into consideration the safety of these guinea pigs. If you dont have enough room as it is it may be dangerous to the piggies if everyone is on top of each other including the piggies.
Also, you know how college kids can pull pranks. Enough said on that.
If everything is cool, get back to us with the best possible dimensions you can find.