I may or may not have been on top of this alleged "Westin" building many times over several recent years. Poked around all over the roof. Saw many cool things, but never saw anything that looked like a transmitter or antenna for 88.7.
That is... if I was actually up there (ahem).
Nit-picking: a transmitter would not be on a roof. It would likely be in a room one or more floors below the roof.
And FM antennas take many forms, from "roto-tiller" models to flat panel ones that look a bit like air conditioner ducts with an antenna element sticking out. Some look a lot like communications service antennas, and not like the typical FM radiator.
Here are a couple of the very different designs: http://www.elti.com/p/18/fm-antennas-and-fm-antenna-systems.html