Boundary wall/terraced house/weatherproof, when not built simultaneously.

we definitely want to "have it built", tend towards the architect, but also have an appointment with the developer.

Developer: Sells a portion of a house together with the land, is the builder, purchase contract between buyer and developer.
General contractor (GÜ): Constructs a house on the client’s land under a contract for work and services and also takes care of the planning. A contract for work and services between builder and GÜ.
General contractor (GU): Constructs a house that is already more or less fully planned under a contract for work and services on the client’s land. A contract for work and services between builder and GU as well as further contracts between builder and third parties (architect, possibly further specialist companies for individual services).
Architect/individual contract etc.: Construction on own land. Contract for work and services between builder and architect covering various service phases and separate commissioning of specialist companies by the builder.
If you have a plot of land, the developer is out of the question. Without your own land, only the way to the developer remains. (Then there is also the wrong hybrid form: purchase of a plot with "developer obligation".)
(This information could also be pinned here after editorial revision by a moderator ;-)).