Architect misjudges clinker facade area

Yesterday we had an interesting discussion with friends who have since abandoned building their house because they were frustrated by it. [...] As a builder, you can't check everything, can you?

The StVO expects a stopping distance of 0 cm
As self-contractors, they will have to advance payment and hold the architect or his professional liability insurance liable. However, the bricklayer did not have to cover the damage caused by ordering too much material and the apparently more favorably calculated profit per cubic meter for the larger order volume - on the other hand, he also did not have to perform the work for the difference.
What makes me suspicious is your introduction: do the friends not want to continue building the fully bricked house to a ready-to-move-in state afterwards???

The house was not completed and sold at a heavy loss. There were many examples like the one mentioned above. They completely lost track and only had problems. In particular, they did not function well together as a team in my opinion. They are now looking for an existing property. The marriage nearly broke down because of the house construction. They are undergoing couples therapy, he is in psychotherapeutic treatment.

We were just at our newly acquired plot and were simply happy that it finally worked out (after so many disappointments). We hope very much that our house construction will not be as bad as that of our friends.

First of all, the contractor is obliged to check the quantities. Then he should have realized that it was too much. Then he can demand a higher price for the smaller quantity. Simply ordering what is stated in the [LV] and then wanting to have everything paid for does not work. He would have been out of luck here. Of course, he can drag him to court and then the architect... but you can always do that.

First of all, the AN is obliged to check the quantities. Then he should have realized that it is too much.

By AN you probably mean AngebotsNehmer? I would not have suspected that he has to check... But thanks for the hint.

Contractor, yes. For example, it is like when the tender states that the bricks should be made of chewing gum. It becomes more obvious who the fool is when that is simply installed.

Too much material delivered, one has to pay, I understand that. But what about the unpaid working hours? With less area, the contractor also finished faster.