I don't have a template, but here are some basic instructions.
1. You need two pieces of 12X12 paper.
2. For the bottom piece, score all four sides at an equal dimension of your choice. It can be 2", 2.5", 3", etc. On one end cut on the scored lines just until it reaches the next scored line. Go to the opposite end and do the same. Then fold in the flaps and adhere.
3. For the top of the box, score all four sides at the same dimension you chose for the bottom, however, make it about 1/16" shorter. This will allow it to go over the bottom easier. Then cut and adhere it the same way as you did the bottom of the box.
Oh, I forgot one more thing. If you want, after you score the top of the box, you can then cut off about 1" on each side so that you see part of the bottom.