This template was created by Debbie Olson and can be found on her blog. This was pretty easy to make. I cut my 12x12 double sided dsp (Basic Gray) to 8.5 x 11 and printed the template right onto it and cut it out. Give it a try, it's a neat little box/card. I would recommend signing the inside flap before you adhere the box.
Thanks and have a great day!