This question has been an enigma for some in the construction industry, yet it begs for the qualification; “it depends on the contractor or designer’.
Most of the consultants I come in contact with here in California, designers are not usually licensed professionals like an architect, engineer or contractor. In most cases particularly found in the custom single-family residential market, the consumer initial calls an architect, and the architect spends hours putting a set of custom drawn plans together to satisfy the needs, desires &taste of the client. It is usually the job of the G.C. (general contractor) to make the domicile a reality.
The term “Design-Build” was coined after businesses that combined in-house design services with in-house construction services under the same entity, in contrast to the “Design-Bid-Build” system.
(work still in progress…..)