A definitive description of the Post-Modern style, if such a thing could be written, would require far more space than is available here, for it embraces a number of substyles or modes and its central principle is eclecticism, the choosing and using of features from other styles – perhaps from two or more in the same design. The most that can be done is to give the building watcher a few hints to help him recognize a Post-Modern building when he sees one. With respect to overall form, one might remember that one Post-Modern architect described his idea l as "a decorated shed." If that fits the building in question, well and good - but many Post-Modern buildings, far from being shed-like, are highly articulated. As for the roof, it may be of any type, rectilinear or curvilinear. Sloping roofs are often, for the sake of effect, of steeper pitch than function would dictate; among the commonest clichés of the style are pyramidal roofs set on square pavilions or turrets and nonfunctional, roofless gables pierced with round holes. The circle is much used for contrast; there may be an outsize round window in the façade.
Whiffen, Marcus. American architecture since 1780: a guide to the styles. N.p.: The MIT Press, 1969. Print.