Prefabricated house in solid construction - Which construction company

A company that lets loose is called a general contractor, abbreviated GU, and usually offers turnkey construction.
Turnkey, however, can mean a lot.
GUs are reluctant to give up trades because own services disrupt logistics (self-inflicted delays, poor planning conditions for the GU, no working hand-in-hand).
Usually, it is painting and flooring, possibly some minor electrical work, that can or even must be done as own services!

Most people who are here in the forum build with a GU. Some still with an architect.
In this respect, the entire range of the forum is available to you – what does not concern building with a GU can quickly be read out.

Best regards in brief

Is there a big difference between GU / general contractor and BU / construction contractor?

I am not sure if and how one can clearly distinguish between them.

An overview is provided on Wiki by the two terms [Bauunternehmen] and [Generalunternehmen].

So every [GU] is also somehow a [BU]. [BU] is not a common term used in discussions here. Rather, in your case, you should deal with the terms [GU]/[GÜ] and differentiate them from prefabricated house providers who do what and how. Even a specialized [GU] can build in the prefabricated house method. Still a lot of jungle ahead of you

A construction contractor can operate as a sole contractor (then he does everything, which rarely happens), but also as a general contractor (then he does almost everything and has only occasional subcontractors involved). A general subcontractor only takes the contract and does not carry out any work himself but acts solely as an agent for all subcontractors he engages. As a home builder, you will hardly encounter a general subcontractor; they are more active in commercial or multi-family housing construction. The prefab house provider usually involves local electricians, tilers, etc., and is thus considered a general contractor, as are many solid construction contractors.

To complete the overview: the developer does not work for clients at all but is himself the client and legally sells the finished developed property (even if he often sells it before construction begins and frequently offers his buyer a usually limited design influence). Developers are almost always solid builders, predominantly on-site masons (but increasingly those who pre-build entire walls in a hall or even manufacture them as panels).

Therefore, you will never come into contact with a developer if you already own the land yourself.

Hm, for me a BU is a regional construction contractor who builds the shell according to the plans of the architect or other procured plans. The other trades are then usually handled through tendering or in the way the BU offers.