Extension of attic in a single-family house

Hello everyone,

I am new here and would like to briefly introduce myself. My name is Bastian, 32 years old, and I come from Baden Württemberg.
Handy with tools, lots of experience in the automotive field (self-praise stinks).
But also renovation, so far I have done a lot myself, screwing, hammering, sawing,... except for electrical (high voltage) and gas-water where it’s better to leave it to the professionals.
However, the new project exceeds my competence, which is why I came across this forum on the internet and am asking for help :)

Now a bit about the situation and the project:

Currently, we live on the first floor of my parents’ house, with our own bathroom, kitchen, etc.
However, due to the sloping roof, we are losing a lot of space. As shown in the drawings, there is another partition wall about 1 meter away from the knee wall, a storage room that is used for "stuff," but would be better usable if the sloping roof wasn’t there.
Because of this, the kitchen is also very small, a small work section; everything works, but it’s not really great.
Above the apartment, there is still an attic where you can only walk bent over.

All the previous options we had eventually turned out not to be options, buying an apartment, etc., so we are thinking about adding an additional floor to the parents’ house.
The goal is to have a full first floor without sloping ceilings, so to raise the knee wall accordingly and to create two small additional rooms with the attic space remaining under the new roof. Access upstairs possibly via a gallery.

We are aware that it is not a cheap construction project, especially not in the current times.
We have already had contact with the city building authority; an addition is conceivable since the other houses on our street are also multi-story.
The neighboring house was extended over 50% of the roof area more than 15 years ago.

After that, we contacted a timber construction company with a supposedly good reputation.
Our wish was to check what is feasible (statics), a draft based on our ideas as well as the documents for the official building application at the city; one should consider a certain lead time.

The first visit and impression were great, all wishes discussed, discussions about the layout, etc.
But then it started that we were constantly put off, no appointments were kept, at some point someone was sent to measure.
The promised drafts and the submission of the offer did not happen, we had to call again, promised callbacks were not kept, emails were never answered. We certainly did not engage in phone or email harassment.
Finally, after 3 months, we were informed by letter that due to the current situation no offer could be made and that we should please contact them again in early 2023 if we were still interested.
Not a word was mentioned about other points like statics or drafts, so we ended things there. Enough complaining for now.

Now we are contacting other companies, possibly also an independent architect and structural engineer.

Since prices are currently extremely dynamic and we have little to no experience, we would like to know what realistic offers are for:
- Architect’s design
- Structural calculation
- Building application or documents for the building application

- If possible, a rough price estimate before such a project based on what has been seen so far?

We are not penny pinchers, better a few euros more for good, clean, and reliable work.
However, I know from my past in the automotive industry that there are always bad apples, as everywhere, who like to "run wild" with clueless customers. I see myself/us in that situation right now, hence the question to the group.

We are grateful for any advice :)

my observation "monentan" is:

EVERYWHERE it is becoming difficult and takes much longer than usual.
As always and everywhere, this will certainly be used or even exploited, but one simply has to expect and cope with very changed conditions "in diesen Zeiten" (after Corona and during the Ukraine war).

-Architect’s draft -Static calculation -Building application or documents for the building application

This is quite easy to quantify: architects generally build according to fee table .HOAI. For a single-family house and complete planning and construction supervision, around 11% of the construction sum is charged as a fee. If you only use the first 4 service phases Basic evaluation 2% Preliminary planning 7% Design planning 15% Approval planning 3% So you pay 27% of the 11%, i.e., about 3% of the construction sum. The architect will then determine the construction sum. The execution planning costs another 25%, so about another 3% of the construction sum. However, the craftsmen work with these plans, or only with these can you really obtain comparable offers. If the architect is also to handle the awarding and evaluate the offers, another 11% is due. If he also carries out construction supervision including documentation, the last 34% would be due. He will probably outsource the static calculations; around 2,000 is realistic. For an extension upwards, I would definitely take an architect and have at least the approval planning done. Have him show you references for extensions he has already done. Alternatively, at least take a good carpenter for the shell construction. Do you want to do part of the interior work yourself? We are talking about 120 m2 gross floor area and a new roof here. Depending on the federal state, I would roughly calculate between 170,000 and 250,000 EUR. Expensive federal states like Bavaria, BW, or Hamburg often call for more. Just briefly on nomenclature: you currently do not live on the 1st floor but in the attic (DG). And the "remaining attic above" is generally called "spitzboden". ;)

Thank you for the detailed answer. We have meanwhile received a rough estimate from another timber construction company based on the plans. We would do the interior finishing partly ourselves, depending on costs. The extension itself, including all exterior work, windows, plaster, roof, roughly 250K. Interior not included. The points with architect, structural engineering, and building inquiry can also be offered separately. Price for this about 7000-8000€.

Is the estimate of 250K with interior finishing or without? If with, the offer or the estimate would be at the upper end after all.