"The Rookery was built in 1887-88 by Burnham and Root. Frank Lloyd Wright was a young architectural assistant working at the time the Rookery was built. Wright had his offices in the building in 1898-99. In 1905 Wright received the commission to redesign the lobby in the building. Wright recast the entryway in his Prairie style and added a sense of modernity through his simple but effective lighting design. Wright's work on the Rookery is his only work on any building within the downtown of Chicago. .." much more in the wikipedia article, en.wikipedia.org/wiki/Rookery_Building
It's said that the term "Rookery" came from which an old building, which stood on this site, was used as an interim city hall following the great Chicago fire. Pigeons became such a nuisance that citizens began referring to the old building as 'a rookery. ' Even when this new, modern and elegant, building was proposed "The Rookery" name stuck.