I have allotted a scale to the building for the purpose of my TS investigation into the fragment, here it is, shown with the Eiffel Tower for scale. I think this is about right for the monumental size of building I am proposing, at this scale it overtakes the Boeing Everett Factory as the building with the largest volume.
Volume = Height x Width x Depth
480 x 240 x 240 = 27,648,000 m3
Over double the Boeing Factory volume which is 13,365,552 m3