Large sheet of heavy duty cardstock, pyramid colour if poss. Draw a square and on each of the 4 lines draw an equilateral triangle (one where all 3 sides are of equal length) so the 4 triangles share their base lines with the sides of the square. Cut out the whole shape and score along the sides of the square then fold the four triangles up to form the pyramid and tape it together from the inside. That's how I'd make one!