[mr_alberta]

This is the cut list that you'll need (taken from the Tank Builder Calculator on Garf.org)

Bottom = 23 1/4 " x 23 1/4"
Front = 24 " x 24"
Back = 24 " x 24"
2 Sides = 24 " x 23 1/4"
Top Front/Back brace = 23 1/4 " x 2"
Top Sides brace = 23 1/4 " x 2"

This is for a "floating bottom" tank (all the glass around the sides are stuck onto the bottom glass rather than on top of the bottom glass).

As for the overflow box, you will be able to use 1/4" assuming it isn't 24" high.