Deviation of actual values from planned values

According to the plan, a room should be 350 cm wide, but is only 335 cm. Would that still be within the tolerance range

No idea what the legal situation exactly is, but THAT is a huge difference. Everywhere we measured precisely, the masons worked with about 0.5 cm accuracy... so it is possible if one wants, therefore I cannot imagine that such a drastic deviation is still acceptable.

I did not measure every wall at our place, but where we laid out, the deviation was usually <4mm, the largest deviation found was around 6mm. With the deviations mentioned by the OP, I would mainly be afraid that the walls are also crooked.

DIN 18202 - Tolerances in Building Construction

The standard where everything should be included.

The permissible tolerances in building construction are regulated in DIN 18202. Table 1 deals with raw construction tolerances. In your case, a deviation of 16 mm is permissible. Now it should be discussed whether a dismantling is proportionate and why the error was not discovered during the initial setting out.

With the deviations mentioned by the OP, I would especially be afraid that the walls are also crooked.

Maybe everything is just smaller, proportionally. Then I wonder: How much concrete and steel in euros does a structural builder save?

An insider once told me about a large car service company where, depending on the car, 100-300 ml less oil than specified is always filled. At liter prices of 30 euros for premium oil, this amounts to several thousand euros per year.

Just trouble!

You should take this as an opportunity to check the external dimensions and important internal dimensions. Then we can talk about savings, but more importantly about depreciation. Just get in touch.