Step 1: Materials
You will also need some tape.
Step 2: Tools
1. Something to measure with (I used a framing square)
2. Something to mark with (I used a Sharpie)
3. Something to cut with (I used a utility knife)
4. Something to help mark and cut straight lines (I used the framing square, but a board would work just as well)
Step 4: Measure and Mark
The box I used was 12 inches tall. I wanted them to be 4 inches tall in the front and 8 inches tall at the back.
Mark the front and back first and then connect the two lines with two lines on the side.