Solid house providers in Hamburg alternative to Viebrockhaus?

This m² calculation is a bit far from reality. Corridors 12m²? Including entrance area, also called hallway? Doesn't work.

Depends on the floor plan. That's why you go to an architect.

12m² for a children's room is borderline small,

I actually find it almost a waste of space. Experience with three own children. 10sqm is comfortably enough.

for a bedroom with double bed and wardrobe it's also too little if you still want to move around a bit.

I don't know how big your beds and wardrobes are or how much you want to "move" outside the bed... And exactly for that reason you either need a planner or just build big and then expensive. Which is not bad, but you just have to be aware that it costs. Both together is not possible - big and extra cheap.

I almost find it a waste of space. Experience with three own children. 10 sqm is comfortably enough.

I think you are divorced and the children no longer live with you?

I think you are divorced and the children no longer live with you?

There were times when we were still married, built a house, and lived with three children and a dog. We did not have the children only after the divorce... Now the children live "only" part-time with me (1/3 of the month).

Since the house has to be placed quite far back on the plot, the floor plan (side entrance, kitchen, living and dining on one side) is also quite unusual.

Then definitely send the plot and the completed questionnaire very quickly!

We already have several offers from different developers, but so far only is an option, since the other two are too expensive (Mollwitz, Breyer and Seck).
Viebrockhaus is financially just barely within our budget, which naturally leaves little room for further adjustments. We would like to get more offers in hopes of finding a provider where we might have a bit more financial leeway. One of the main reasons why Viebrockhaus is attractive to us is that many things are simply well thought-out and prepared, so that we as builders don’t have too much effort. (We have 4 small children and our time and energy are also resources we have to keep an eye on).
It is important to us to have solid construction, reliable and transparent planning and communication, and preferably a very transparent price calculation (based on actual measures), and definitely a truly solid construction and quality, preferably without botched work on site and without needing to be there every day to supervise.
We had considered and asked for an offer from Kagebau. was also on my radar, but I heard more often that as a builder you apparently have to handle a lot yourself (official procedures, etc.).

On your plot, they cannot act as developers but possibly as general contractors. Professionally, I work as an independent building advisor and as an architect and builder searcher. Two minutes on their websites were enough for me to clearly see that Mollwitz customers undoubtedly belong to the very uppermost class, whose piano teachers and cleaning ladies build with Breyer and Seck. Both are several octaves above the income of the clientele of Viebrockhaus (ordinary senior employees entitled to company cars, mid-sized town lawyers, specialist doctors without their own clinic). If you are looking for a competitor to the affordable but not economy provider Viebrockhaus "from Ratiopharm," Kagebau and Team Massiv should at least be playing in the right league. Collecting more candidates for a request round before making a decision is not productive.

We have a 99% chance of having a plot and want to build a single-family house here, one-story construction (gable roof with dormer or preferably townhouse) without a basement with 225 sqm, 5 bedrooms, 1 office, 2 shower bathrooms, 1 full bathroom. [...] Do you think there is still an alternative that would be interesting for us? Or are our demands in terms of quality, price, and service just too high or unrealistic? Do you have any other ideas or suggestions?

I don’t know your plot and am hypothetically taking the specified key values literally (purely out of politeness, certainly not out of conviction). Then I see a single-entrance two-family house (you can simply leave out the apartment doors for now and connect the utilities to a common meter) with each a normal family apartment (i.e., two children's rooms), the upper one with a second bathroom above the technical room on the ground floor. Take a look at my "House Building Roadmap, also for you: the HOAI phase model," then complete "Module A" with a freelance architect and make a decision during the waiting period. I would not be surprised if the preliminary design ends up being about 180 sqm (laymen always plan a bit clumsily; from experience about 20% of “invisible” surfaces result from the untrained eye, which however clash with the budget). I will only be “on duty” here in the first half of the week for the time being (but reachable via the comment channels of my online practice).

Mittelstädthaus from Himmelpforten, Schlüter Bauregie from Harsefeld, Zimmerei Noll from Tostedt, Effinger from Seevetal, Team massiv from Büdelsdorf, Tünjes&Meichsner from Bösel, Lübberstedt from Winsen/Luhe, Eco-System with several locations, Dammann-Haus from Wohnste. I am not familiar with the north.

Until the start of construction, that is correct for Team-Massivhaus. After that, it depends on the commitment of the site manager. (In our case, it was really good (Schleswig-Holstein).
One should mention, however, that the authorities in Hamburg and SH know Team-Massivhaus and know that they like to send off the (amateur) builders. I encountered a lot of patience there.

You just have to ask and badger a general contractor. Often their offers are included in their exposés. Later, the builder no longer thinks to simply ask them. They don’t come forward with their service offerings on their own.

As I said, with Viebrockhaus we already have a variant that is within the stated budget.

Do you have an offer including the builder’s positions including the brick cladding or just a sum x, how much the designed house variant will cost according to the construction specifications?

We have 700,000 for the house construction

I would say: one might not believe it from Viebrockhaus, but it is possible.

Since the house must be placed quite far back on the property, the floor plan (side entrance, kitchen, living and dining on one side) is quite special.

When I read something like that, my nonexistent neck hairs stand on end.

Why .must. this, why .must. that? Isn’t it more that one .wants. to make it complicated for oneself?
Because: "(side entrance, kitchen, living and dining on one side)" is certainly not special!

P.s. I would also go to an architect.

You have already been to the architect (Mollwitz).