Offer for the closed shell construction - reasonable?

Hello dear community, I have a question for the experienced members and would really appreciate an answer, as I can no longer make progress with my own research.

I have bought a plot of land and now want to build a house on it (single-family with 2 granny flats). The house should be fully basemented (WU concrete basement), KFW55 and otherwise standard 08/15.

Currently, I have living areas of 189m² for our half (of which 79 for the basement) and 86m² for both granny flats together in total.

The offer for the closed shell includes the following services, but without individual prices:

- planning and application, - staking out and earthworks, - soil probing, - the full basement as WU concrete on sub-slab insulation 10cm WLG 035 and interior walls made of sand-lime brick, - masonry as aerated concrete outside and inside as sand-lime brick, - plaster facade with 18cm WVS, - reinforced concrete ceilings, - roof truss made of KVH wood (gable roof 45), - stairs and basement entry in the exterior area, - windows as triple glazing ug0.6 according to WK2 and also a front door

I have omitted minor details for readability.

According to the offer, €406,338 are due, thus €1,476 per m².

This seems somewhat high to me, or is this appropriate for a closed shell including basement?

Thank you very much for your efforts

Edit: this is only about the shell construction..
For that, it is really quite expensive.

I would definitely obtain at least 5 offers. For a closed shell construction, that is too expensive. Most common mistake: too few offers! There are drastic price jumps and that has nothing to do with quality.

only shell construction, earthworks + basement way too expensive.

For the pure shell construction way, way, way too expensive
We have 300 sqm of living space + 70 sqm basement + double garage (including ancillary rooms)... Structurally and in terms of execution, our house is not exactly simple and we are paying about 300K euros for the shell construction (including earthworks). We had 4 offers on the table and did not choose the cheapest one...

But I read something in your description about the roof structure, windows, and front door? Is all that included now or not? That actually doesn't belong to the shell construction. What about roof panels and roof insulation and so on?

Then the whole thing can look different... You basically can't say that in a general way... For a normal building, I would say it's still too expensive. With corresponding window sizes, quantities, and materials, it can certainly turn around...

P.S.: Just to stay briefly on the windows, the triple glazing with Ug 0.6 is actually meaningless for the window. The glass is the cheapest part of the window; the frame is where the money is. Definitely ask for the Uw value and definitely the material (I assume plastic windows). Also ask for the surcharge for Ug 0.5, which is usually not high at all.

Actually does not belong to the shell construction.

It says "closed shell construction". Although the roof is not covered, right? Is it not sensible to award windows, door and roof truss separately? And then get 3 to 5 offers only for the shell construction (and possibly also the basement separately)? Who created the design? What does he say about the offer? How did the joint tender for exactly this package come about?