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.

Not a clue what it is your really trying to do.
Got a picture of that opening?
Not sure how cutting a differant angles going to help.

No there's nothing to take a picture of yet.

Doesn't really matter what I'm trying to do, just wondering if there's a tool to do what I'm asking

Yes, a common feature of miter boxes is the ability to cut any angle from 45deg to 0deg, or maybe even from 45 left to 45 right, or bigger angles.

Of course power miter saws have adjustable cut angle too. Mine will cut 60deg left or 50deg right I think.