Complex sentence: Most of the charity's income is from rent collected on the New York Fifth Avenue skyscraper the Piaget Building, which was built in 1978 under the Shah, who was overthrown in 1979.
Split into simpler sentences: Most of the charity's income is from rent collected on the Piaget Building, a skyscraper on Fifth Avenue in New York City. The building was built in 1978 for the Shah, who was overthrown in 1979.