Cost estimation Bauhaus style

Hello,

I am new and would like to present my project. My property is located in the northern Ruhr area and is already owned.
We have been to the architect and initially presented a wish list, but quickly came to the conclusion that we need to make compromises to reduce the price.

No bricks, no hip roof, garage with utility room from a prefabricated supplier, self-built patio roof, etc.

Now I can provide the following details about the house.

180 sqm living space
Ground floor: Large living, dining, kitchen area with rustic windows on the ground floor, utility room, guest room, bathroom
1st floor: Gallery, two children's rooms with children's bathroom, bedroom with master bathroom and dressing room, laundry room
Geothermal heat pump with a chimney system (water-carrying)
Above the 1st floor no second concrete ceiling, but wooden beam ceiling (architect confirmed cost savings with the same airtightness)

The house is to be approximately square with a flat roof (2 degrees) without greening Window area downstairs (motorized blinds), 1st floor roller shutters (electric)

Own work except material: Electrical, tiling, painting

What is your estimate of what it will cost, how does the architect calculate? We have no results so far and are curious about your tips?

Where is there potential for savings?

Bauhaus style means to me the actual look from the outside. They say it is more expensive, so we can also call it a modern 2-story house. After a lot of internet research, I still do not understand what makes the price more expensive for a Bauhaus style, maybe someone can explain?

What would help me more than 2500/sqm would be the indication for individual trades, roughly estimated

Savings potential: omit the [wasserführenden Kamin].

Yes, and also geothermal energy. Either gas or air heat.

Total price without land will be around 400,000 plus additional construction costs plus kitchen and garden at approximately 500,000 euros.

Tutti kompletto as wrote, I also see the 500k€. Your information (standard and further details) is far too vague to name a price for individual trades. Many positions you probably don't know yourself yet, so it will always remain incomplete until the tender is awarded. An approximation is indeed a flat rate per sqm of 2k€ without ancillary construction costs, outdoor facilities, garage, and kitchen. But only if you stay within a standard like air-water heat pump, pitched roof, controlled residential ventilation, electric shutters, possibly a normal fireplace, etc. The standard mentioned above excludes such frills as basement, children's bathroom, geothermal heat pump, green flat roof, Z-lamella blinds everywhere, 5m lift-and-slide door, etc. What you wish for should actually be provided by your architect for a first cost estimate.

What I don't understand: why is a flat roof cheaper instead of a hip/gable roof? Not here. And why not greened? I wouldn't have wanted to execute it without...

I also hardly believe that a flat roof is supposed to be cheaper. Especially what happens if it ever becomes leaky and the beams get wet...