Middle English bilden, from late Old English byldan "construct a house," verb form of bold "house," from Proto-Germanic *buthla- (source also of Old Saxon bodl, Old Frisian bodel "building, house"), from PIE *bhu- "to dwell," from root*bheue- "to be, exist, grow." Rare in Old English; in Middle English it won out over more common Old English timbran (see timber). Modern spelling is unexplained. Figurative use from mid-15c. Of physical things other than buildings from late 16c. Related: Builded (archaic); built; building.
In the United States, this verb is used with much more latitude than in England. There, as Fennimore Cooper puts it, everything is BUILT. The priest BUILDS up a flock; the speculator a fortune; the lawyer a reputation; the landlord a town; and the tailor, as in England, BUILDS up a suit of clothes. A fire is BUILT instead of made, and the expression is even extended to individuals, to be BUILT being used with the meaning of formed. [Farmer, "Slang and Its Analogues," 1890]
"round building," especially one with a dome, 1680s, from Italian rotonda, typically in reference to the Pantheon, the most celebrated building of this kind, from noun use of Latin rotunda, fem. of rotundus "round" (see rotund). Meaning "circular hall or room within a building" is from 1780.