What Foster said, though singles don't need boxes as long as there are other cedar boxes in there.
Sometimes you don't want the cigar to pick up cedar so it retains it's intended taste (though probably rarely), but cedar is also used to help retain constant humidity. In this case, several boxes in there will help accomplish this.
If you do build your shelves out of cedar, I would remind you to put holes or slots in them.
Have fun. I love mine, but slight temp. problems in my area necessitate a fridgidor.
Sooooon.