Draw a square that is 6 inches by 6 inches on a piece of cardboard and cut it out.
Draw a 6-inch line on a piece of cardboard and then draw a dot in the middle of the line, 3 inches away from each end. Draw a line at a right angle from this line that is 5.19 inches and connect its end point to the endpoints of the first line to make a triangle. Repeat this three more times to get four equilateral triangles.
Test fit all the pieces and make any adjustments if necessary.
Glue together triangle one with triangle two, then glue together triangle three with triangle four so that you have the square base and two pieces that are glued together.
Get someone to hold the two pairs of triangles together as you glue them to form the top of the pyramid.
Glue the square base onto the four triangular pieces that have been glued together.