What would you do differently in the next house construction?

This is a very important matter. Not only necessarily to document "material defects," but also to know later:
- where the electrical lines are located
- how the underfloor heating is installed
- what the wall/ceiling structure looks like
- where the supply/disposal lines are on the property
- what is connected where (drain, etc.)
- etc.

Additionally, you can nicely see how the house develops. I always find it amazing how especially the living room and bathroom evolve during the course of the construction.

I have to agree with you on that. I have documented everything with us, every room every day and what was done outside. Always good to know where what is and how it was installed (ventilation, heating, all lines, wall connections, seals, etc.)

I would also give myself more planning time.

You just need a municipality that doesn't like your construction project (never happened before, we don't want that, it's never been done, and anyway, we don't like it) and - voilà - you have almost 2 years for planning!
However, you shouldn't count the wear and tear on your nerves.

The advantage is really that we were able to think a lot about everything, visit many trade fairs, trades, exhibitors, and all that without having to make an immediate decision.
On the other hand, we lost almost two years in which we kept paying rent longer, and we also missed the sensational low interest rate for financing (KfW, for example, has meanwhile risen significantly).

But: as of today, the approval is certain! The municipality will not file a lawsuit at the administrative court, and WE ARE FINALLY ALLOWED TO START BUILDING!!!!

Congratulations, I’m happy for you, even though I don’t know you. But I’ve experienced bureaucratic madness quite often in my life. Don’t ask me how I feel about civil servants.

Congratulations, I’m happy for you, even though I don’t know you. But I have experienced bureaucratic madness several times in my life. Don’t ask me how I feel about civil servants

Without it, you would very likely be surrounded by tall buildings with your single-family house.
If there is a development plan and one adheres to it, there should be no problems.

If there is a development plan and you stick to it, there should be no problems.

There isn't one always and sometimes that's actually a good thing... just thinking about what our municipality now wants to create as an inner-city development plan makes me shudder. Bavarian Disneyland is all I can say. Building will then only be allowed as it was 100 years ago (the size of the windows is restricted, for example), no innovations possible anymore, a floor space index that doesn't take into account that building land in the Munich metropolitan area is scarce to nonexistent, etc. So a development plan is not always a blessing.
(we fortunately are not affected by it)