Cost estimate single-family house ~175m^2, 3-story

Hello,

we are currently determining an approximate guideline price for our construction project.
Land is available, approx. 1000m^2
I have already received an offer from 2 master builders (acting as general contractors) and both gave me a quote (both relatively similar) that was about 2800-2900€/m^2. (Without garage, basement, or any special equipment)
I am now trying to find an approximate guideline price where I would end up if I contract everything separately myself.

Expectations:
* 3-story (nice view, not yet sure what goes on which floor, yes I am allowed to build three stories)
* approx. 150-160m^2 living space. The 175m^2 mentioned below is gross floor area. We wrote down all the rooms we would like to have, each with square meter size, and this is how we come to 150-160m^2.
* Controlled residential ventilation & geothermal heat pump (ring trench collector, this is becoming quite established in Austria)
* High ceiling height (In the example calculated with 330cm clear shell construction height)
* Parquet floors (we really like high lamella parquet ("industrial parquet"))
* Large window areas facing south, lots of fixed glazing, few doors/windows to open
* Open room structure (e.g. living-cooking-dining area)
* 2 children planned
* I plan some own work, but want to calculate costs and financing assuming zero own work
* Land is fully developed, lines run in front of the property
* As low EKZ (energy consumption index) as possible, if possible passive house (does not have to be "certified")

I got an offer from Combi-Box for the "shell construction" and am now trying to complete this with estimates for the other trades. The shell consists of a steel frame construction with 10 cm PU sandwich panels where the windows are already factory-installed.
If I have calculated everything and it all works out, I will go to a planner to get a reasonable floor plan.

Construction site would be Vorarlberg/Austria.
Prices seem to be a bit higher than in Bavaria. The average architect house is currently being built here at 2700-3500€/sqm. But I am about 15km from the German border, so if, for example, floor layers in Germany are significantly cheaper, I can also look there.

Cost estimate:
House 175sqm gross floor area, 3-story (top floor half), with walkable flat roof and ~72sqm basement.

Connections:
Gravel area for carport (carport planned almost directly by the street): ~2000
Water/sewage: 2500 (fee to municipality, what does the connection to the house cost?)
Electricity: 3519 (fee to utility company, what does the connection to the house cost?)
Gas: 0 (to utility company, would only be for "security" in case I want gas later, what does the connection to the house cost?)

Earthwork:
Excavation (storage on the property), clean layer, string framework for basement, backfilling excavation on the property etc.: 15000

Shell construction:
Basement (raw basement, 10cm insulated, solid against penetrating water, no light wells/external staircase): 50000
Shell (steel frame modules, 10cm PU insulated, incl. window installation): 96144 (offer price)
Roof structure/roof covering (excl. insulation): 16000
"Making roof walkable": 8000

Windows and doors:
Front door: 6400 (1 piece)
Interior doors: 10000 (10 pieces, solid wood with installation)
Fixed glazing: 12000 (170€/sqm, is that too little?)
Venetian blinds: 8000
Various other shading: 2000
Patio doors: 5600

Sanitary installation incl. rain or well water use, 3x WC, bathtub and 3x shower: 17500
Electrical installation: 20000
Heating incl. installation: 15000
Underfloor heating: 5000
Controlled residential ventilation: 15000

Interior walls finishing:
Installation layer (approx. 280sqm exterior wall, 30€/sqm): 8400
Additional drywall interior walls: (70€/sqm): 9800
Wall coverings (where no exposed wood, painted, stone, etc.): 10000

Interior floor finishing:
Subfloor (filling etc., 20€/sqm): 4900
Screed (anhydrite, 45€/sqm): 11500
Tiles (25€ material, 65€ tiler/sqm): 6500
Parquet (25€ material, 25€ laying/sqm): 7600

Interior suspended ceiling (45€/sqm): 7900

Kitchen: 15000
Stairs: 5000
Lighting: 2000 (bulbs etc., rest in electrical)

Insulation + facade:
Additional exterior insulation (55€/sqm): 11500
Roof insulation (35€/sqm): 3200
Wood facade: (70€/sqm): 15000

Outdoor facilities are planned at a later date except:
Carport (kit): 2000
Various minor outdoor items: 3000

Miscellaneous:
Rough floor plan planning: 2000
Plan submission, energy certificate, submission plan, construction management (shell), building permit, execution planning (shell): 2400 (flat rate, in offer for shell)

TOTAL: approx. 445,000€

All material + installation.
What did I forget, where did I underestimate, where overestimate?

Thank you very much

The connections to the house are included in the flat rate in D. This will probably be the case with you as well.

Sanitary and stairs I find too low, parquet material as well

Best regards in brief

I find the sanitary and stairs too low, also the parquet material

The stairs are included in the shell construction offer like that.
For the parquet material, I took the prices from some online shops and marked them up a bit.

What would you estimate for sanitary?

Thank you very much
Daniel

The staircase also seems to me to be set a bit too low. It certainly also depends a lot on the shape, type, material. Our offer for an oak staircase is currently still twice as high. However, there is still room for negotiation.

The only "real" offer I have is for the shell construction, and the staircase + temporary steps are included with €3800 (2 staircases, ground floor/first floor and first floor/second floor). I would actually like to cover the staircase with the same parquet as the floor and have therefore rounded up to €5000.

Do you think €1200 for laying the parquet on the staircase is too little? (excluding parquet costs, these are included under the item "Parquet Material")

First of all, you have parquet waste, furthermore you have to add: impact sound insulation, possibly substrate filler, working materials like glue or whatever, skirting boards. I would add a total of half again to the material cost, possibly equipment purchases. I am not familiar with material prices, but you should weigh whether to order important items online or buy them from a specialist retailer.
He who buys cheap buys twice, as is well known.

Covering a stair step also means setting rails on the edges, which are not cheap and the installation should not be underestimated.

The basement stairs cost nothing?

In short, regards