I used a 2" aluminum pipe that I cut into 3.5" lengths for the hubs. Metal strapping will go through the center of the pipe and 2 wood screws will hold it together on both sides of the 2x4 beams.
Dome construction started in the garage until it got too large. Then we moved the operation to the back yard.
The base was set on concrete blocks at each corner then the two half dome sections were placed on top.