Bec asked how we made the polypipe bend in a circle. The answer is -- with great difficulty. When we built the original dome with its 3 concentric circles I remember that my daughter was helping me with the smallest circle. We each held one end of the pipe, and tried to bring the ends together to form the circle. As we got close, so the pressure was too great, and the pipe sprang back, knocking my daughter over. Bruce eventually managed to connect the two ends with a piece of wood.
When we had the huge winds that wrecked the original dome, the pipe did indeed buckle, and even though we straightened it out, it never looked the same. The geodesic dome that we built as a replacement is much better, in that the pipe doesn't have to bend so much. In addition, there are a lot more joins, so the structure is more stable, and the top is flatter, so it's easier to arrange a tarpaulin over the top in such a way that the chooks are well protected.