Yamasaki is known for his proposal of the space-use concept, his notion of an urban university free from distractions. The board of governors of Wayne State University appointed him as architect of the College of Education Building so that the main campus's first building would be worked out with those tenets in mind and designed specifically by him. Thus, Yamasaki created a building with windowless classrooms in an inner core, along with elevators, stairs, restrooms, and other service facilities. Glass-enclosed passageways and offices surround the classroom block on the upper three levels. The exterior wall of the building consists of 120 structural precast-quartz-aggregate-surfaced, reinforced-concrete “trees” (columns and spandrels), each forty feet high and spaced five feet apart. Anodized aluminum sash forms narrow, pointed windows that contain gray sheet glass. The exterior wall of the lower level is set back ten feet, and a loggia or arcade encircles it. The recessed top level has four roof gardens.