Cost bungalow (220m^2) with rooftop terrace

What you need to plan for will be told to you by your architect. Don't trust him? Is he officially commissioned - I ask because of his compensation, which seems more like a friendship price (assumption: service phases 1-8, all amounts gross).

I find the surveyor quite high. Various other costs are pretty low. Except for earthworks, no incidental construction costs are visible.

We had wished for the entrance concept like this after our trip to Scandinavia, large open spaces with maximum daylight.

I feel like I'm on "You Have Been Warned"

I find 320,000 too little - the floor plan is a small disaster: after entering you are in a dark tunnel! Not even space for the coat is planned
Living rooms facing north and the children have to shower without daylight.

...Edit: and then you also have to go through the living room first. that's not practical at all!

So should I rather add the typical 10-15% on top?

From gut feeling: yes. And plan an additional buffer for sample patterns, extras, and unforeseen events. What about the ancillary construction costs?

after entering, you are in a dark tunnel! Not even space for the coat is planned

I think you enter the building on the lower floor.

I think you enter the building on the lower floor.

You might be right, I considered the chamber as a (non-accessible or non-furnishable) pantry. But this access would be even worse than the main entrance – then all the shoes and jackets would be collected in the kitchen???? The architect who submits a building application for this should have their license revoked!!!

Well, it is at least unusual. The living area is more than large enough to place a wardrobe. It is an open area that needs to be divided accordingly. This room layout is known from holiday homes in Scandinavia, and people there don’t really mind it. Of course, not everything that is enjoyed for 2 weeks a year has to be good.