sentences:  The building's surface was made out of concrete to reduce the cost, inferior to the stone finish that Wright had wanted.The small rotunda (or "Monitor building", as Wright called it) next to the large rotunda was intended to house apartments for Rebay and Guggenheim but instead became offices and storage space.In 1965, the second floor of the Monitor building was renovated to display the museum's growing permanent collection, and with the restoration of the museum in 1990–92, it was turned over entirely to exhibition space and christened the Thannhauser Building, in honor of one of the most important bequests to the museum.