Unclear statements construction service description, explanation required

Hello,
I would like to build a house - with a construction company. The planning is going quite well so far, but I am bothered only by the unclear statements in the construction service description.

Here are a few examples:

Reinforced concrete slab "up to 20 cm thick, according to static calculation"
Flat roof executed professionally
Floor slabs up to 20 cm thick, according to static calculation
Tiles "Numerous options are available from our contract partners... We will provide you with some dealers after contract conclusion"
Interior walls up to a wall thickness of 24 cm, aerated concrete or calcium silicate according to static calculation
Gas condensing boiler "Brand device from Buderus, Vaillant, Junkers or similar"

Now my question: Is it normal not to know exactly what you will get before signing the contract? Or should one try to clarify the above-mentioned things before contract signing?
Despite multiple inquiries, I only receive standard answers from my contact person, in which he refers to the structural engineer, the construction service description, or other trades.

Best regards

Hello,

at least for the topic of tiles, you should be able to get a price per sqm.

For the heating, the exact type mainly depends on the framework conditions (living area, hot water demand, etc.).

Basically, I would try to fix as much as possible already in the contract.

We quickly weeded out developers who were not willing to agree to this.

Best regards,

Dirk

Base plate, floor slabs: if the structural analysis says more than 20 cm must be installed, then an extra charge applies (I don't know if 20 cm is the standard) Tiles, as Schnaggls says! Also, up to what size does the installation apply? Usually extra charge from 30 x 30, meaning: for 30 x 60 there is an extra charge. We inquired! For us, the cost is the same. However, that did not apply to the wall tiles :( The joint color was even mentioned in our [Bauleistungsbeschreibung]!! The gas condensing boiler was also only calculated during construction for us. You can have the [Bauleistungsbeschreibung] checked. Then you will know what else might be coming your way ;)

There is nothing more to add to that.