Building a house is more complicated than thought - constantly new prices!

No, I do not expect that. I only uploaded the offer in case someone might be interested. But not with the request to extract the relevant points for me.

I briefly looked into the [Bauleistungsbeschreibung]. It's just the simplest standard.

Examples:
- Gas heating with radiators: Is this OK for you? Due to the current situation, I would tend towards a heat pump. Underfloor heating is a must for me, especially in connection with the heat pump.
- Electrical is also not generous at the moment. Since we will be adding quite a bit. First of all, power outlets! Network is practically non-existent. Photovoltaic preparation? Cable for wallbox?

And this probably runs through the entire [Bauleistungsbeschreibung].

I only read one page and I also noticed that everything is just the cheapest possible.
ESSAY roller shutters
Made of plastic
And for me the worst: with a crank (for larger windows).

Otherwise, it also said something like the builder is responsible for safety.
What kind of costs will come up for you, for example? These can be pitfalls.
Construction electricity/construction water is also your responsibility (but that is usual).

Besides, someone already wrote to you that the problem is the things that are NOT included.
Building drying?
Rubble container? Disposal?
Construction fence? .....

I also built with Heinz von Heiden and there were no exorbitant additional charges. Everything was settled from the beginning. Of course, held in check during the sampling. For example, with the staircase, communicated directly with the executing company. That way, cheaper and got more for less money than it would have been during the sampling. I can't say anything bad about it so far.

Since I basically want to build a log house, [...] Specifically, it concerns the following models: Town & Country "Raumwunder 100" as well as Heinz von Heiden "Bungalow, der Unverbesserliche B760"

Those are a coupe and a convertible; apart from the catalog price (and both being miles away from your "Plan A"), they have no significant similarities.

Then I wonder whether it makes sense not simply to take an older house step by step into core renovation. And then work with the materials currently available.

In the song "Huusmäister Kaczmarek" by the Bläck Fööss it says "Hammer kääne Hammer un finge mer kään Zang, jo dann nemme mer zur Nuud de Isestang". I see you in a used house in the same situation as with the new build, just with a different object. The trades where you need specialists are the same — and so are their schedules. And you cannot tile your bathroom with roof tiles just because they happen to be available ;-)

Town & Country "Raumwunder 100" as well as Heinz von Heiden "Bungalow, der Unverbesserliche B760"

Both are budget GUs that don’t have to be bad, but also don’t offer much in that price range.

I have the written offer from both manufacturers here. The only things I still have to do are laying tiles and putting up wallpaper or buying a kitchen.

No, that is not correct. There are still quite a few items left. Just the earthworks plus removal of soil can/will be five-figure.
And as I read it, you have no calculated ancillary construction costs.

So far, I have not signed a purchase contract here.

It would be a contract for work and services, you would be the client.

The bank had already told me in advance that I would have no problems with the loan amount I need.

Has it received a complete calculation from you or only a financing amount from you, which however is unknowingly incomplete?

These two prices mentioned can by far not reflect the actual total costs.

That’s right.

I have not noticed anything that could be missing.

Then look at something obvious, for example: sockets. Bathroom. Could the attic be accessed? No? With additional costs, yes. Landing in front of entrance? Paving? That belongs to the yard work items and has nothing to do with the house…

Well, I just reread the construction service description of the offer I have and could not find anything that suggests that I will have to pay more for something I didn’t plan for in the end.

What should a layperson notice that he has to paint all the wood outside himself, dispose of the soil, possibly also pay for containers and portable toilets? It could be that scaffolding is also no longer included now…

The entire business model of these two companies is based on getting as many expensive follow-up orders as possible later because the builders do not know what is missing.

I wouldn’t quite agree with that. The house with catalog price works. Why should they include higher-priced extras already if that reduces the target group?
You also configure a new car: most don’t need a trailer hitch, but seat heating would be nice if it fits the budget.