Pardon my ignorance. If I build an earthbag dome house, given the roof itself seems to be made in the same way you build the walls, does this mean I get to save on the roofing costs compared to a flat roof structure ?
You can likely save a high percentage comparitively on materials. This will be offset with increased labor though. What is your time worth? Bag work and plaster work over say 8 foot high takes longer. I run a hoist off my scaffold for moving buckets up high.
This could total to a fair amount of cash saved, but if you are considering small roof square footages, run the numbers for all the costs (framing/sheeting/roofing/insulation/ceiling/bond beam). When dealing with smaller spaces, a proper roof may be within your financial reach thanks to the small quantities. Consider if an EB dome is appropriate in your environment.
We built our earthbag home with beams going from wall to wall on a 19ft span in the master bedroom. And a center white oak post (12" diameter, 9ft tall) in main living area with a wagon spoke like center fanning out. Both have worked well! The beams were purchased at a local saw mill. 4" x 8" thickness. The beams were about $30 each