Take thin plastic or heavy paper, cut out a circle larger than your tube, cut a straight line to the center of the circle. Overlap the 2 cuts until you get the desired height you want. Glue the overlap. I glued on strip polystyrene as ribs. The small water tower is a toilet paper roll with Japanese toothpicks glued on the outside and heavy thread for the bands. The large tower is made with 2 CD's, top and bottom with thin plastic wrapped around them to give you a perfect tube, The rest of the structure is polystyrene. The two milk tanks are 1 1/2" plastic tubing with precision board glued to each end and sanded to the shape I wanted.