Well, to be honest, I'm not sure if it's actually for sale, but the owners of foundation for the Chicago Spire skyscraper would probably be willing to entertain offers from motivated buyers.
I have every confidence that this Calatrava designed building will soar towards the sky at some point in the near future. However, I was never that excited by the design. Skyscrapers fill me with a sense of wonder, but not as much as they used to. What I find frustrating about high rises is that the experience of space inside them is almost thoroughly horizontal. Cathedrals and train stations, which have a predominantly horizontal circulation program tend to express a vertical spatial experience much more effectively than tall buildings. Some towers have impressive internal atria, but they tend to be subordinate to the relatively narrow floor plate.