Entry into the project "New Construction"

All good! It is always good to name ideas and listen to counterarguments. That is what a forum is for.

Wanted to prevent misunderstandings.

What I take away from all the posts is, among other things, the fact that a regional contractor does not have to be more expensive.

Are there any who know such contractors from the Cologne/NRW area, where one can also inquire?

For this reason, it may ultimately be a non-KfW/KfW70/KfW55/KfW40/KfW40+ etc...

Plan and build YOUR house according to your requirements and not those of a funding bank. If you then reach a standard through small AND FOR YOU sensible changes that gives you a financial advantage through funding, then YES. However, you should already detach yourself from such partially phrase-like used parameters at the beginning or at least not focus too much on them.

Fundamental thoughts regarding [Mutter] are sensible and maybe attractive for both sides if you see this as part of your shared way of life; but not for reasons of funding. Often something like this is not concretely discussed or calculated with [Mutter]/[Vater]; maybe this would lead to a completely new consideration of your building project if desired on both sides.
But you should then implement something like this with someone who acts more freely than the mentioned house building company, possibly better with a local, more flexible provider.
Regardless of tax and funding considerations, this can be implemented within an affordable framework through clever planning.

If a seller wants to have a construction contract signed without a concrete, inspected, and notarized secured property at the latest simultaneously... What do you think yourself, is that serious? People, I thought the grandchild trick was audacious. But here it is completely legal. They don't pretend to be the lost grandchild but to have the dreamed plot of land. Only no one gets to see it

Entering into a construction contract without having a property would, in my opinion, even be a fraud of entering (Eingehungsbetrug) on the part of the builder, since he would be accepting that he probably objectively cannot fulfill his part of the contract at all. A property "service" from the provider probably even saves him from jail *LOL*

I have to "strongly" disagree with you. Unfortunately, I cannot yet present complete figures, but from the numbers so far and from a "gut feeling" I would say the surcharge for KfW40(+) is under! the amount of the subsidy.

Do you also take into account the additional financing costs for the luxury of "playing landlord"?

and that is exactly why I am grateful for any kind of support and suggestions from the many experts here.

When it comes to the term "experts" I want to exempt myself; I am allergic to that word. I always associate it with some Prof. Dr. complete idiots spreading their nonsense on Sunday evening talk shows.

Are there any who know such entrepreneurs from the Cologne/NRW area, where one can also inquire?

I have "lost track" of which regional general contractors we have already discussed here, but the Cologne area will certainly not be a blank spot. Browse here once in the moderated section "Experiences with XYZ Construction." About which place 40 km from Cologne are we even talking: a concrete, but rather fixed place 40 km from Cologne, or any place within a 40 km radius around Cologne (possibly also the Deutz side), so BM/BN/GL/GM/SU/EU?

Remember, if you include the [Einliegerwohnung] as a rental apartment with income in the financing, it is quite possible that the bank will also want to see tenants.

No, this should be calculated from the beginning with an income without rental income or similar.

Depending on how much patience your chosen GU has, he should simply implement his proposal for you as an example. You specify the framework program for rooms and areas, and the GU creates a floor plan with a granny flat and without. Then it becomes clear whether it is worth it.