Property development - basement yes or no?

It would certainly have looked different with a prefab house provider.

Would it? How do you come to this "more certain" assumption?

For me, it was also important that the general contractor takes care of almost everything. Earthworks, energy consultant, architectural services, construction power.

Opinions can differ.
For example, it was more important to me — and it turned out to be an advantage in hindsight — to have an independent civil engineer for earthworks.
Construction power...? Anyone can organize that themselves. In my case, I even saved 800 EUR because I was simply allowed to use the neighbor’s construction power.
Energy consultants and architectural services are included as standard anyway with most large prefab house providers I know.

Depending on who you ask or where you look up the information, the difference between GU and GÜ is
Either: The GU takes on at least one trade really by themselves with their own craftsmen and the other trades are just subs, while the GÜ basically just subcontracts everything and basically only does the construction management, coordination, and planning.
Or: The GU executes according to a given plan, while the GÜ also takes on the planning.
In my usage, I follow the first definition, because otherwise almost all GUs would be GÜs, which to me is too little of a difference.
Also, I have personal satisfaction knowing my GÜ in a smaller *Gemein*schaft, since it essentially consists of probably only two to three people. Then you can somehow gossip about them better without generalizing too much.
I have to say: The GÜ referred to himself as a developer, even though he definitely built on my property.
A freelance employee of the GÜ meant the side of the GÜ with "bauseits". Both are for me clear indications that the greatest competence of at least this GÜ does not lie in construction. In this respect, I may be influenced in my opinion regarding GÜs and this does not have to correspond to the average competence of the representatives of this guild active in the market.

Energy consultants and architectural services are included as a matter of course with most major prefabricated house providers known to me.

Both Schwörerhaus and Weberhaus naturally list the architect as part of the construction. Certainly, you can save a euro or two if you commission such things yourself. But then you have to take care of it yourself. And as the builder, you are responsible, for example, that the surveyor arrives on site at the right time.

Would have? How do you come to this "more certain" assumption?

On the one hand, the prices for promotional houses have practically exploded. 25% is quite common there. On the other hand, I remember that we once talked to Weberhaus about the subject because the development was still in progress for us. The representative mentioned something about a fixed-price extension of, I think, 1% per month. After one month, I would have already exceeded what my general contractor offered. Even if it was only 0.5%, more than 1500€ quickly accumulates.

We have not spoken with Schwörerhaus / Weberhaus because we lack the installation level for both. For all providers with whom we have already had appointments, the ancillary building costs (earthworks, construction electricity, etc.) were not included, but the architectural services were. Whereas the prefabricated house expert, for example, also believes in having the house planning done by an independent architect and then going to the general contractor with the result. But that may also be due to their business model.

Thanks! I can well understand the first explanation. I feel a general contractor is better. Only I imagine subcontractors to be difficult, as one probably has no say in the choice of the subcontractors.

If you want a basement and the prefabricated house provider does not offer that - would that be a dealbreaker in the selection?

From my point of view, clearly yes. By analogy, this applies to floor slabs no less than to basements: always include it in the scope of responsibility of the house supplier.

We have already spoken to an architect who was recommended to us many times and has a reputation for being very accurate with his cost estimates.

Haha, basically approved ;-)
Then take him, it doesn't get better than this!
(if he is not so good at designing, the pale purple floor plans are back again).

We understand that upcharges can be a pitfall,

"Upcharges" and "re-upcharges" logically only exist where the general contractor (GU) regularly assumes his own construction service description. This excludes (regardless of the construction method) all major providers right away. But with an architect, it makes sense to always make your own construction service description.

We make sure that the price guarantee is longer than the construction time guarantee.

That is also true for every construction method – be careful of the effect ;-)

2. with individual contracting: here one (or the architect) makes a tender according to the wishes and then awards the individual trades to the craftsmen with the best offer

Two essentials regarding this: 1. A tender with individual lots does not exclude GU offers. 2. What the best offer is can only be found out with a professional tender – proper quantity takeoffs and such are the be-all and end-all.

Prefabricated house manufacturers are also just a special variant of general contractor; the basic principle in solid construction is the same. What is decisive, however, is that on the one hand the usual standard corresponds to your desired standard and on the other hand that you also make few upcharges later. These are relatively expensive with the GU. [...]
Long story short, just because something carries "prefab" in the name, does not mean it actually is. And a price guarantee always depends on what exactly is included.

Glue this immediately into the poetry album!

Sorry, I have actually used prefabricated house provider synonymously with GU :).
So our favorite is to build with GU/general contractor with work (GÜ) (what is the difference there). [...]
Also happy per PN if not desired here.
We are always happy about recommendations.

Then give a contact method (mine can be found here by searching "11ant gmx"). Prefab houses and turnkey houses can already be thrown in the same pot, the "work by the builder" delta is basically the same for both. Your preference should preferably be "none," let the tender results guide you.

The GU actually takes over at least one trade with their own craftsmen

This is basically due to craft law reasons. The most widespread type of GU is a builder as a master mason and concrete worker, but there are also mailbox GUs (who call themselves GÜ as architect-GU – but there are also some with their own crews).

We have not spoken to Schwörerhaus / Weberhaus because both lack the installation level for us.

Please don’t dream that this would mean that cables can be easily retrofitted later!

Although the prefab house expert also holds the opinion to have the house planning done by a freelance architect and then only go to the GU with the result.

Within the masonry house scene, that is indeed the best way; with "prefab" house builders (regardless of wall material) it is rather unrealistic, then the timber house only works with the freelance carpenter (or else the architect has to know the system well).

I feel a GU is better. Only I imagine subs are difficult, since you probably have no say in the choice of subs.

If you really want to select the contractors who actually do the work, you have to tender individual lots (and then even exclude GU) – but I see no overall advantage for first-time builders.

But as I said - solid construction is not completely off the table.

There are also prefabricated house providers in solid construction.

I would like to point out, although it may not be enforceable nowadays, to look for a company that offers preliminary sampling. The sentence "Changes to ..... are reserved" is included in every building service description known to us and grants the house builder/house supplier enormous leeway in their favor.

Furthermore, you cannot rely on seeing something you like in a show house or a brochure of the house builder/house supplier being actually executed. For example (--> I am only giving one example), we did not have it explicitly guaranteed that we would get a tiled shower floor; why would we, it is nowadays, in our opinion, standard, was visible in the show house, and in our view no unusual request. Apparently it is. We had expected an extra charge, but not that we simply would not get it, "We don't do that." Well, we are not getting a tiled shower floor but have to take a shower tray ... I do not want to sound bitter, but in the meantime I am just glad when the house is warm, has running water, and a place to cook/sleep/shower. ;-) And fortunately, it was never about a house but about moving to a region we love. :)

The difficulty is probably that there are no (?) providers who offer sampling before the contract is signed.