Firstly, a good roommate should be compatible. Students have to face with a lot of stressful things when coping with academic subjects in their classes or dealing with a new environment. They desire their roommate be an understanding and dedicated person, with whom they can feel more relaxed and comfortable whenever they are together: talking, learning, or even moaning. Also, living with a roommate who has many things in common would be more ideal for them, making their student life, which seems very challenging and laborious, more meaningful and memorable. It also helps them avoid lots of trouble. For example, they want to study in quite dorm-room, but their roommates often listen to loud music. It would be very annoyed and disturbed for them to bear their roommates for a long period of time.
Secondly, responsibility and honesty are two other good characteristics of an ideal roommate. Living with a lazy and irresponsible roommate during a year would be a disaster, ruining the meaning of their student life. Let's try to imagine that a roommate who never lifts a finger to do chores, although they seem very simple things--cleaning a bathroom or tidying up his studying corner, for instance, or never be self-imposed to pay room fees. Moreover, everything worsens when they lost the trust at their roommate. They will never be rested in their mind, thereby cannot focus on their study, while their roommate often stole their assets or refuse to accept their faults.
Last but not least, a considerate roommate makes students at home. Homesick is a common challenge that a student, especially a rural and provincial one, has to deal with when they live their first time at universities without daily caring of their parents or siblings. A considerate roommate would be a savior for them. He or she can together with them share hardships and happiness. Furthermore, when being with their ideal roommate, everything would be better for them in difficult circumstances, especially when studying and living far away from their home, whilst they are still young and inexperienced.
For the aforementioned reasons, an ideal roommate should be a congenial, trustworthy, and considerate person. Living with a complete stranger would be difficult and troublesome at the first time, but I think with a good partner, they will together overcome every obstacle in their student life.