Compare Rows To Determine If Column Values Are Different?

I need to determine if a value for a group of rows is the same or different and I am not sure where to begin. I am fairly new to writing T-Sql code. I am working with SQL Server 2005. This is a work assignment; I am not a student.

I have two tables: One for Course and another for CourseDays. As the Course table implies, it lists courses for a school. The CourseDays tables has a row for each day a course is held. For instance, one course maybe held on Monday, Wednesday, and Friday, so there would be three rows, one row for each day. A given course could be held in a different room for each day. I am trying to write a query that returns one row for each course, and if the room number is the same for each day the class is held, return that room number in the row, else return 'Various'.

Course table:
CourseID, Desc
1 English
2 History
3 Science

CourseDays table:
CourseID, Day, RoomID
1 M 320
1 W 445
1 F 680
2 T 123
2 Th 123
3 M 514
3 T 514
3 W 521
3 Th 901
3 F 521

Expected results:
CourseID, Desc, RoomID
1 English Various
2 History 123
3 Science Various

I simplified the example, as there are about 30 columns in the table and about half a million rows.