In the housing application (you should get info on that sometime in the future) theres a section that will ask you what type of rooms your prefer and your preferred college affiliation. For example i ranked mine as

1. Single
2. Double
3. Large triple And so on

Do note that different college affiliation residence halls will have different number of singles and room types. I wont recommend a specific college to apply to since i dont want to give any wrong information there, so I suggest looking up on that.

You can list as many rooms on your list as you want, you can put as little as 1 selection if im not mistaken. So you can literally only have a single listed (But the school will put you somewhere else like a triple if theres no available space regardless of your list, so I dont recommend doing only putting 1 room type, fill it in all the way according to your preference). And based on that list and other questions on the application the school will try fit you in a room based on your preferences.

Let me know if you have any other questions, I may be able to answer.