n. Purchasing the materials required for a repair or renovation that one has hired a tradesperson or other professional to perform.
2010
The gap between hands-on DIY activities and handing over an entire project to a building contractor is shrinking because consumers are opting for BIY — buy-it-yourself.
2009
China's new middle class tend to buy their new apartments as shells, and then kit them out themselves…It is less DIY, however, than BIY: Buy-it-Yourself. New homes need fitting out from floor to ceiling, a job that only professionals can do.
1987 (earliest)
BIY is where consumers buy the materials for professionals to fit.
The 1950s were a hobbyist's paradise with magazines such as Mechanix Illustrated and Popular Mechanics showing the do-it-yourselfer how to build a go-kart for the kids and how to soup up his lawnmower with an actual motor! In fact, the term do-it-yourself didn't enter the language until the early 50s, and the abbreviation DIY (upon which the abbreviation BIY is based) soon followed. (My use of the male pronoun here is intentional; this was mostly a man's world, which is why the term do-it-herselfer — a woman who does her own repair and maintenance work — didn't bubble up until the late 1980s.)