The building is composed of two distinct parts: the train station itself and the 18-story tower. The roof height is 230 feet (70 m). Ideas as to what the tower was originally designed to include a hotel, offices for the rail company, or a combination of both. In reality, the tower was only used for office space by the Michigan Central Railroad and subsequent owners of the building. The tower was never completely utilized; the top floors were never completely furnished, and served no function.
http://en.wikipedia.org/wiki/Michigan_Central_Station
I'm afraid the answer is somewhat political, considering that this building represents the last gasp of the Gilded Age - a monument to the egos of the robber barons. It is a nice building, however.