A cardboard box is a great starting point for building a pyramid. It already contains a square bottom attached to four equal walls. All that remains is for the walls to be cut into the proper shape and folded together.
Find a cardboard box. The bottom should be a square. The top should be easily removable. And the sides should be at least the size of the bottom.
Cut off the top of the box without damaging the sides.
Measure one of the sides of the box at the top edge. Then make a mark directly in the middle. Make marks in the middle of the other three sides as well.
Cut from the midpoint to each corner of the box on each side. When you are done, you should have a square bottom with four isosceles triangles for sides.
Fold the four triangles together until they meet in the middle. Use glue or tape to join them.
Draw any bricks or other decorations you want on the sides before you cut. It will be harder to do after you've made the pyramid.