It would hold exactly 512 cubic feet of water. A spherical tank measuring 5 feet 6 inches in radius will use all 384 square feet of material, too. Butt will hold 707.6 cubic feet of water-195.6 cubic feet more than the cubic tank. Again, both tanks used the same amount of material, but the spherical tank used it more efficiently. A dome, therefore, will always use less material to cover the same space utilized by a 'square' conventional building.
Less material means less cost, or higher quality materials for the same cost, or both.
Domes are energy efficient. To illustrate one aspect of the energy efficiency, think about the tanks we have just built. Obviously, the square tank would, because it has less water to remove. Energy works in a similar way. The heat in the tanks must radiate through the material.