Last month I painted a section of my son's bedroom wall with chalkboard paint. I knew it would look better with a frame around it, but I really didn't want to deal with the hassle of a miter saw.
So I made a very simple frame out of MDF boards. You can see that the corners aren't mitered. The boards just butt up against each other.
The boards were attached to the wall with finishing nails. I haven't painted the frame yet, because of my darn tennis elbow. It would have been easier to paint it before hanging it, but I often like to take a simple project and make it more complicated and time-consuming.
Case in point: my son's monogram that I stenciled in chalk. Guaranteed that will be erased before the day's end :)
Oh well, at least the frame gives the wall a much more finished look. And, it's a handy spot to keep the chalk!