Once the vertical saplings are up, horizontal ribs are placed around the frame. The ribs are spaced every 2-3′ or so. These ribs strengthen the structure, and help the vertical saplings to have roughly the same curve. Most ribs were put up the weekend of 6/30, and were finished the weekend of 7/4.
This picture is taken facing NE. Note the door in the east side of the frame, the bottom horizontal rib is missing between two vertical saplings. The door is about 5′ high.
Another picture of the top, with horizontal ribs in place.