Twenty-sided dice, or D20, are central to the mechanics of Dungeons & Dragons and many other role-playing games. The dice are shaped like regular isocahedrons, with 20 triangular sides. You can make your own 20-sided dice out of paper. Depending on your dice-making skills, these may be too uneven to use in an actual role-playing game; however, if you replace the numbers in the D20 template with your own pictures or designs, they can make great ornaments.
Print Bruno van de Casteele's D20 pattern (see Resources). Cut it out carefully with scissors or a craft knife.
Make a crease along all of the lines marking the flaps and the divisions between the triangles.
Attach the flap on side 14 to side 20 using glue or double-sided tape. (If you're using glue, wait for the glue to dry between each side before moving on to the next.)
Attach the flap on side 15 to side 5. Your die should be in the proper shape, but with a large, jagged hole in it. One side of the hole should have four pieces without flaps (17, 13, 9 and 2), while the other side should have three pieces with two flaps each (3, 19 and 12) and two pieces with one free flap each (7 and 15).
Attach each piece without flaps to the two flaps surrounding it. This will get progressively more difficult, because when you reach the last piece, you won't be able to press the flap and piece together from the inside of the die, and when you reach the second-to-last piece you'll have a difficult time maneuvering.
Print the D20 pattern on sturdy paper, such as photo paper, to make it easier to attach the pieces together. Small folding errors can result in great difficulty fitting the last few pieces together without bending them. You might have to make a few dice to practice before you can fold them accurately. You can make larger or smaller 20-sided dice if you save the template to your computer, open it in a photo editing program and adjust the size. Make sure it's the right size to fit on a piece of paper, though.