Cut and fold part A, which will form the seat. It is made of multiple 11.5" diameter circles folded over each other to make a strong sitting surface. The narrow strip is folded around the circumferance of all of the circles to hide the edges.
Cut and fold part B, which is the weight-bearing element in the stool. It is just a large sheet that is rolled into a tight cylinder. You can make folding easier and more precise by using a straight edge and a blunt instrument to score parallel lines into one side of the cardboard. The cardboard will then fold nicely along these lines.
Cut and fold part C, which is mainly decorative. This piece has thin diamonds cut out of it, allowing the middle to be pressed in when it is rolled up. The result is an hour glass shape.
Test fit the parts, and then start gluing things together. It will look most impressive if none of the glue is visible.
Let the glue dry fully before you sit on the stool. If you have built the stool well it will be quite sturdy, but you should sit fairly still. Tilting or leaning will wear it out quickly.
(2009). How to: Make a Cardboard Stool. Retrieved from http://www.trunity.net/upcycling/view/article/143228