Pretty simple setup. Just fold all the flaps together as you would normally and tape all of the seams. When cutting out one of the panels use a utility knife and make sure that the two notches that would normally hold the clothes hanger are on each side. Cut the top off and wala, cheap brooder...
If your looking for an inexpensive brooder go to Home Depot and grab a tall wardrobe box $14. I taped the seams and cut out one side and now my chicks have a 24"x24"x45" brooder and are really happy. I bought another one so when the time comes I can make it a double wide haha