Maybe you could use GPS'd H2's with robotic ditch-witches on 'em. Head on out to the salt flats in Utah, and make some skyscraper molds. Convert some fire trucks to spray an epoxy / carbon fiber tow mix, and voila, instant carbon fiber skyscraper panels. Fly 'em in, raise 'em up, bolt 'em together. Could be used for bridges, too...
A thought for anyone who says the salt flats aren't flat enough- remember, you could always convert a steam roller into a GPS'd surface grinder....
Just think, 85 mph rapids!!!