late Old English hrost "wooden framework of a roof, perch for domestic fowl," from Proto-Germanic *hro(d)-st- (source also of Old Saxon hrost "framework of a roof, attic," Middle Dutch, Flemish, Dutch roest "roost," Old Norse hrot, Gothic hrot "roof," of unknown origin. Exact relationship and ulterior connections unknown. Extended sense "hen-house" is from 1580s. To rule the roost is recorded from 1769.
1520s, from roost (n.). Related: Roosted; roosting. Chickens come home to roost in reference to eventual consequences of bad actions attested from 1824; the original proverb seems to have been curses, like chickens, come home to roost.