Freshman girls either stay in the 3rd floor of Ross, or in Schwitzer. This year Butler has seen the largest freshman class in its history - as in EVER - so there has actually been some tripling of a few rooms. You can request to live in the Residential College (aka "ResCo") because they have single rooms there, but that's an upper classmen dorm, and there are select freshmen living there due to overflow and if people have special needs (allergies or physical disabilities, usually) so I don't know how things will be next year. If you do decide to come to Butler and you do the random roommate drawing, on your housing request forms, be totally honest with the kind of person you are. If you're really clean and want to live with someone else who's really clean, put it that way.
Also, most dorms have roommate agreements that you fill out individually and turn into your RA's. They're basically just request forms for things you might not be comfortable asking straight on, like "if you eat my food, will you please buy me something to replace it?" or "please don't use my hair straightener without me asking", and you go over them together with your RA.
Not to mention, having a roommate is one of the biggest factors in the whole college experience! It's about stepping outside of your comfort zone - you've lived in a single your whole life - why not have a roommate? Plus, it's really nice to have someone to come home to. If you get along, which most people do, it makes it that much better.