Divide and develop plots themselves

Ok, the necessity of the preliminary building request and the anecdote are sobering, but not too surprising.

Not necessarily. Although I strongly advise against developing a binding land-use plan yourself, in June the extension of §13b of the Building Code was decided, which makes it easier for municipalities to draw up land-use plans under certain conditions. With a bit of luck, a group of prospective builders might find an open ear.

With this approach, it is not yet clear to me how to put this into practice. Outer area plots that meet the requirements of §13b probably exist much more often than building gaps. So do I first talk to the relevant municipalities and try to find out in principle whether they are "generally" open to the concern and then look for properties in the municipalities? Or do I first search for (arbitrary?) specific properties (of which there may be some), talk to the owners, and then with the municipality, only to find out that they have no interest in drawing up a land-use plan "for us"?

You will at least be the one with the least influence.

Or do I first look for specific plots of land (of which there might possibly be several) arbitrarily, talk to the owners and then to the municipality, only to find out that they have no interest in preparing a development plan "for us"?

No, not arbitrarily - and I would also rather look for wasteland than in areas that are still on the outskirts. Unfortunately, you cannot yet contact me via PM here (but you can take a look under "Information" on my profile to see how to get in touch anyway).

I would also rather look at fallow land than in areas still classified as outer zones.

Where we - for me - would come to the problem of distinguishing a fallow land (of sufficient size) from the outer area within the inner area. Thank you very much for the kind offer, I will write an email during the day.

So I first talk to the municipalities in question and basically try to find out whether they "basically" have an open ear for the concern and then look for land in the municipalities?

Yes. The greatest difficulty here is probably finding the right person who is at the same time citizen-friendly, influential, and professionally competent. This can range from a council member in the building committee to administrative personnel from department heads to clerks. Lots of work - but no pain, no gain. Two years ago, I would have said "Forget it." With the recently passed Land Mobilization Act, politics has created a dilemma between housing shortage and limiting land consumption. It remains to be seen how each individual municipality intends to deal with this in view of staff and financial shortages. In any case, I see a small chance for your project.

Exciting project or adventure .... :-)

8 couples are 16 individual personalities with 16 different wishes, opinions, preferences, etc. These 16 people interact with each other, although presumably everyone loves each other, one couple might get along a bit better with this or that couple, one couple wants 5 kids, another has already given up on that and would rather have a Rottweiler in the garden, the next one gets seizures from children’s crying ....

And all this with a planning period of several years. I would bet 1:1000 that during this time one or the other couple will drop out because
1. they got a great opportunity somewhere
2. they separate
3. they no longer get along with one of the other 7 couples
4. they feel overlooked in the planning and division
5. they no longer want a Rottweiler
6. half of the couple got a great job offer in Wanne-Eickel
and so on and so forth.

Then there is the inertia of decisions, 100% of votes are required for every decision. And since it can be assumed that when buying a plot of land every couple has to immediately contribute liquid funds ....

Oh, and it should still be Cologne/Düsseldorf. Maybe Munich as an alternative? :-)

With 8 couples needing maybe 350 sqm of land each, that’s easily a plot of 2,800 sqm. Such large plots are certainly much more sought after than small niche things, every builder will just put down 8 city blocks there and be happy about 8 x €700K.

No, I consider the project not feasible.