The Mitchell Domes in Milwaukee aren't geodesic domes (which means cut off of a sphere). They are beehive shaped, which is closer to being a paraboloid than a spherical section. The area you provided is really dependent on the internal layout (the floors) so it doesn't really factor into our thinking.
A paraboloid is a three dimensional shape whose cross-sectional shape is a parabola (just like the cross-section of a geodesic dome would be a circular arc).
The volume formula (which you can derive with just a tiny bit of calculus) is simply
V = (pi/2) r2 h
where r is the radius and h is the height. Use your figures to come up with a volume estimate, but remember that a beehive shape looks sort of paraboloid, but I'm not sure that's in the blueprints!
Stephen La Rocque>