The evolution of the exterior skin of the Lever House, Seagram Building, Citicorp, Lipstick Building, Ford Foundation and the United Nations buildings were all born in a very similar manner due to the fact that they were built after world war II where steel was starting to be used as a building mechanism.
The Lever House and the Seagram Building have very similar skins. Although the Lever House is a bit bulkier than the Seagram Building, they both have a very similar shape and assembly shown through their rectangular glass figures and by having an outdoor plaza. The only difference being that the Lever House is elevated off the city block while the Seagram building has its plaza just a bit above ground through a couple of steps to give the building a sense of awe when approaching it.
Both the Lever House and the Seagram Building also resemble a lot of what the United Nations Building has. The main gem of the assembly has the same shape as the one of the Lever House and the Seagram Building, having a rectangular shape with glass curtain walls. However, the alignment and precision are seen mainly in the Seagram building and on the United Nations Secretariat building. The Seagram used its mullions as a sort of aesthetic component to be displayed on the outside at equal distances from each other along with the close attention to the color of the overall building which has a dark and yellowing burnt tint on the glass. The United Nations Secretariat building used its material of concrete to give that organized and elegant gesture just like the mullions used on the Seagram Building. The Seagram building also used concrete to make a statement in architecture but in a different way by placing two big masses of concrete to create a division of space seen in the lobby area where the cores are placed.
The Citicorp building has a very heavy and robust look to it just like the Lipstick building but in a different shape. However, the same idea of lifting the building up to create commuter space at the city street level played a part but in a very drastic way as compared to the Lever House, but served the same purpose. Similarly, the Citicorp building, the Ford Foundation building has very prominent columns shown on the outside of the façade. The main difference is that the Citicorp building used metal panels as a form of spandrel and glass curtain walls for the rest of its façade, where as the Ford Foundation building used glass and steel and a big open space inside the building rather than outside for commuters.