You'd need a pretty big vacuum. My shop vac can hold about 20 gallons and fits in a corner of my basement, so I can't imagine how large one would need to be to

You'd need a pretty big vacuum. My shop vac can hold about 20 gallons and fits in a corner of my basement, so I can't imagine how large one would need to be to fit a skyscraper in there. I guess that's why they call them Dyson Spheres though.