What you ask is possibly not something that can be determined with any accuracy. If you see a destroyed or damaged building, how do you determine what percentage of its destruction or damage was due to bombing, what to artillery/street fighting, and what to happy/drunken Soviet soldiers after the battle was over shooting off their guns for the hell of it? (Examples of this last form of destruction by U.S. troops can be seen in several places in Munich, for example.) Certainly there is still a lot of destruction and damage in Berlin (and Leipzig) that was subject to benign neglect by the D.D.R. government during its reign.
Post-war, the U.S. Strategic Bombing Survey determined that Dresden was 61% destroyed by bombing; Magdeburg 59%. They are widely considered the greatest damage done by non-nuclear bombing attacks, and topped the U.S.S.S.B. list, although the small city of Zerbst was allegedly "about 80%" destroyed by bombing in April 1945. I am unsure of the criteria used in that survey.