Cost estimation for construction project and feasibility

For a house in the Braunschweig area, that seems a bit too much to me.

As much as the southern residents here calculate, it won't be that much for BS either.
Take a look at the smaller regional construction companies.
But always calculate generously rounded up – it will definitely be used. And if not, then you immediately have a special repayment rate.

Whether the prices are more or less in the south, north, or wherever doesn't matter. You can inquire, plan, and finance that. Usually, the problem is that various additional building costs are forgotten. They unexpectedly make it expensive. Or special requests. But I think Thomas310 is on the right track for now.

We will deal with local developers and then see where the price journey goes. I think we have a good reference point for now.

Very good, maybe you'd like to keep us updated.

You don't (!) have to. For example, in our case, it will come down to significantly less with the same size (but 2 full floors with a hipped roof) and even if I took your land price, I would "only" end up at about 500k.

500k might be ambitious, but up here I also think it’s feasible. We have 160 sqm KFW 55 and converted to your land price at just over 500k, but with the 2016 price list. Our general contractor currently has a 150 sqm gable roof for about 190k in the price list, reasonably equipped, e.g. with underfloor heating, centralized controlled residential ventilation, and with simple earthworks you’d probably be at 250k, including floors. Take a look around among acquaintances who they built with, which companies have construction signs in construction areas around you. The ones you mentioned are all prefab house manufacturers; here in the area they might be about 5%, the rest is done by many local companies. For us, the prefab house suppliers were also at least 10% more expensive in the final price.

The price for turnkey projects ranged between €230,000 and €300,000, at least within the range we have in mind.

From the top edge of the floor slab or inclusive?

Plot including all costs (real estate transfer tax + notary, fully developed): 160,000
Construction costs: 150sqm*1800€/sqm = 270,000€
Double garage, brick-built with direct access to the house: 25,000€
(Construction) incidental costs (kitchen, garden, furniture, etc): 30,000€

Construction costs 150sqm, 270,000 I find realistic
Construction incidental costs 30k are not realistic. For us about 107k, without great demands.
Plot 160,000 you were very lucky. Where?? Is there school, daycare, work, sports, doctor, pharmacy, shopping, playground, transport connection, ... nearby? For us for 1050sqm was 315,000eur, plus broker notary tax clearing demolition.

Perhaps one could clarify what each person understands by ancillary construction costs, or what they see as included or considered within them.

Plot of land, it would be interesting to know where the investment location is.

Beautiful plots can cost 40,000 euros in the Altmark, 600,000 euros in Hamburg or Berlin.