House construction / house purchase planned, evaluation of financing plan

Payment plan: [Makler- und Bauträgerverordnung]

Doesn't matter: the original poster is buying a house, not the builder themselves... when does one pay then? Also according to the construction schedule?

Depends. If this is a developer deal, then according to the Broker and Developer Ordinance. A large chunk is due right at the beginning for the land, regardless of the actual land value. A big problem with the Broker and Developer Ordinance is that you massively overpay and have no leverage if things go badly.
However, it sounded more to me like a linked deal, meaning the original poster buys the land and has to build with company X. Then there is the land once, and independently of that a semi-detached house from the company according to the payment plan. In that case, the construction start in autumn might be optimistic anyway if you are simply scheduled normally.

Thank you very much for the numerous responses.

Here is a rough overview of the finances:

- 160,000 euros developed plot of land
- 310,000 euros prefabricated house (ready to move in including base slab), will probably get a bit more expensive during the selection process
- 14,000 euros incidental purchase costs for the plot (we are buying the land and house from separate companies, so we are the builder ourselves) – but in the worst case, the tax office may want land transfer tax for the house after moving in -> about 20,000 euros on top
- 10,000 euros prefabricated garage (yes, I don’t need a huge, masonry double garage, especially since the garage may only be 3x9 meters max anyway)
- I have the details at home, but incidental construction costs were around 50,000 euros (earthworks, development, driveway, further details "performed by the builder himself", etc.; fortunately, the garden is sponsored)

We will pay for kitchen, furniture, small stuff, etc. out of savings

Is this calculation so unrealistic?

Ok. Didn’t know that.., has it always been like this? Or am I mixing things up?
Doesn’t matter: the OP is buying a house, is not the builder himself... when do they pay then? Also according to building schedule? I maintain: most people underestimate these costs, including here.

No, we are the builder ourselves. The payment schedule is as follows: plot due this summer, house paid in three installments (after each phase), I think shortly before the assembly of the prefabricated house part is due, another part afterwards. However, not according to the realtor and developer regulations.

but in the worst case it can be that after moving in the tax office wants property transfer tax for the house again

Not in the worst case but regularly. The guys and girls from the tax office didn’t just show up by chance. And of course you are obliged to present the assessment truthfully.

10,000 euro prefabricated garage

Do you already have an offer for that? That seems very low all-in to me.

Oh yes, the house is of course not built by a developer, which is why the real estate agent and developer ordinance does not apply - but the building code does.

Do you already have an offer for that? It all-in seems very low to me.

Yes, have a look at DuroB... (probably not allowed to mention the name), there is a configurator. I come to 8,458 euros including delivery and assembly for a prefabricated garage 2.95 meters x 7.95 meters including electric garage door and rear door. Then add the base slab and you are at around 10,000 euros.

Oh, those are those metal boxes. That is, of course, something else. :)