Think about all the people (your peers, mentors, the first generations around you, even professors in your new department) that might feel marginalized by your question. You might as well change the topic to "Chinese roommates" instead of being obscure about it. To be honest, regardless of how you phrase that question, it's going to sound somewhat offensive. There are all kinds of people in every culture and there's always some sort of trend to tag people based on their origins, but it doesn't work like that. Even if you don't get along with someone, they probably have a couple of good qualities that you would appreciate. Don't let someone's cultural background or nationality prevent you from seeing those good qualities.