While I have used a pizza box to demonstrate the technique, I've also had very good luck with 2 mm matte board from the art store. The matte board is stiffer and nicer looking than a pizza box.
I have not made any allowances for the power plug, but a simple hole in the crossbar will allow the plug to pass through. Feel free to modify the design to your own taste.
On to the first step!
Step 1: Print out the pattern
Try printing the larger one first and if it gets cut-off on the edges, then use the smaller one.