Expected construction costs in Hessen: architect vs contractor

1800*320 = 576,000€. Additional construction costs approximately 35,000-55,000€.

If the normal connection costs are about 6,000€, can we probably multiply by 3 here?

Outdoor facilities, such as paving, garage etc. are not included yet and will come later.

If we accept the rate of 1800€/m², neglect the necessary extra stairs and assume 15,000 for outdoor facilities and paving and 25,000 for the double garage, then according to your calculation it is
576K + 55K + 18K + 15K + 25K = 689K

The preliminary inquiry resulted in a loan of 480,000€ with 20 years fixed interest rate at Commerzbank currently at 2.51% with a monthly rate of 1,849€.

But with that amount, we probably won't make it with the desired house

"Probably" not, because even with the conservative calculation without reserves and extra expenses, 200K is missing. And that is a difference for which you don’t need to trim anything, but a new concept. Strange that one doesn’t realize that oneself.
Add up your installments, scale that to the new construction sum and consider whether you can/want/should afford that as repayment.

Costs everything between 500-900k

Don't you have a pot of gold somewhere looking for a new owner?

But good counterquestion from you, a home builder in Bad Vilbel asked me the same today.

"The first question you have to ask yourself is, CAN you afford that much money?" "If yes, the more important question would be whether you also WANT to." The former probably not with over 500,000K, the latter definitely no. We will now do as many here have suggested and adapt the house to the maximum budget and not the other way around.

Thank you very much for now.

How about following a [Minimalprinzip] instead of a [Maximalprinzip]...

Set up a room program with minimum requirements. So not what you want, but what you have to...

Don't you have a pot of gold somewhere looking for a new owner?

But good counter-question from you, a homebuilder in Bad Vilbel asked me the same today.

"The first question you have to ask yourself is, CAN you spend that much money?" "If yes, the more important question would be whether you WANT to." The former probably not with over 500,000K, the latter definitely no. We are now doing it as many have suggested here, adjusting the house to the maximum budget and not the other way around.

Thanks a lot for now.

if you don't want to call for 500k you should deal with construction prices and adjust your wishes to reality.

How about following a minimal principle instead of a maximal one...

Set up a space program with minimum requirements. So not what you want, but what you need...

So really, probably only need 80 ground floor, 80 upper floor, 60 attic

Then the dream of a 50-60m² living room fades

if you don’t want to call up 500k you should deal with construction prices and adjust your wishes to reality.

500K just for the house wouldn’t be an issue. I would even grudgingly manage to come up with that somehow (want to). Just a bit more is rather not. And with the 1800 formula, I would already end up at 540,000€ just for a 300sqm house. Without additional construction costs and others. Although with that amount you have to ask yourself whether 100,000 more or less really makes a difference? Then I’d rather build myself a real dream house with 40 - 45, you live for a while in your first built house and learn over time through the forum and from owning a home. They say the first house you give to your enemy, the second to your best friend, and the third is supposed to be yours.