Did a little math here, to get a 90,000 square foot ballroom, you need a structure 250×360′. Turns out the Treasury building across the street is 250′ wide and a little long. A little google maps measurement and GIMP magic, and we get…this:

Umm, that’s freaking huge. I tried to keep the frontage aligned with the remaining west wing. The renderings I have seen look like a pretty normal 25,000 square foot building, not the something the size to TWO American football fields, with the end zones.

Something just does not add up, unless they plan on making this 3 or 4 floors…no idea how this is supposed to work.