General procedure / schedule

But I also didn’t want to have €100,000 of unplanned expenses on the clock after the sampling.

You decide for yourself how big the surcharge for the sampling is. Set aside a reserve for "sampling" and use it up during the sampling. You can do a bit of internet research on the things to be sampled, then you’ll have an idea of the prices.

Even if the company now let you look through the sampling catalogs, you still wouldn’t know how much the things will cost in a year. There are only rough guidelines anyway. And you can look those up yourself too.

Honestly, I don’t understand all your stress. Plan a reserve, set priorities, decide, and pay.

I don’t understand your concern regarding the selection either... through internet research, questions at the show home of our construction company, and ultimately the information in the contract (which you receive some time before signing), we had a fairly clear idea of where we wanted to specify upgrades and where we would probably be satisfied with something without extra cost or only expect minimal additional charges. In the end, it worked out, and the extra costs themselves were not excessively high, in our opinion, so we could live well with them. If you assume €100,000 in additional costs for the selection, you have definitely looked in the wrong price range for the general contractors.

But I also didn't want to have €100,000 of unplanned expenses on the clock after the sampling

The amount is quite utopian. Reserve + self-discipline is the keyword.

So I got the add-on catalog from a company - we were at a total of 3,500 euros more.

It also depends on the company. With Viebrockhaus you spend less on add-ons than with Team Massivhaus.

The sampling is intended to select this, that, and the other. Basically, re-sampling is financially more manageable than up-sampling. If you have already up-sampled this and that, you should only re- or even down-sample the other - otherwise it will be too expensive. If you basically want an A4, then buy it directly from Audi, because if you go to Seat instead and up-sample the Leon to an A4, it will unfortunately cost like an A6 (if not even like an S6). If you want a frameless glass shower and huge tiles, then the corner window must be put on the chopping list. Confusing Bemustern with Aufmustern is regularly punished with pharmacy prices.

€100,000 was taken as an exaggerated value so that it is clear what I mean. I thank everyone for the input. I will get in touch when I have feedback from the providers.