I am all for saving the planet, and I like the advantage of living underground, but the embedded cost, pollution, and harm to the environment a structure like this would cause would blow your mind. Are you going to use concrete? How about the rubber membrane for the roof? Don't forget about the heavy equipment used to dig the hole, and massive amounts of top soil lost! How much land would a company have to destroy if they couldn't use their 80 story building? Instead of a small footprint urban spraw would be a disaster. I think that there are plenty of options out there, but you better consider the big picture.