JBFC

I've just moved back to Cleveland after being out of town for a few years, and am starting to follow the Medical Mart project closely. This question might have been answered already, but is there any reason the new CC / MM would have to be built underground if it were to be built on the current site? I know people talk about consistence with the Group Plan, preserving the Mall, etc, but wouldn't it be cheaper to build above ground on the mall? Is there a law stopping that?