mitre saw or box

Do all mitre box's cut to a 45° angle or do some go bigger? Or can u get a mitre box that has lots of angles?
I want to frame a box for the ceiling going down the stairs and 45° will work but I'm 6'5 and a little more head space would be nice, not sure what angle I want though so something with different angles would be best.
I know I can put the wood with the cut side against the wall and make a bigger angle but don't like doing that.