Cost of self-managed homeownership

Hey,
I want to build a house in about a year.
My budget for the house is around 100,000€.
I did some rough calculations and would like to hear some opinions on it.

The house should have a floor plan of 7 x 14m and be about 4-5m high.
This gives me an area for the:
Walls: about 200m²
(Pitched) Roof: about 100m²
Floor: about 100m²

For the costs of the walls in timber frame construction, I calculated as follows (price/m²):
KVH (60mm x 230mm): 13€ (for 2 linear meters/m²)
Insulation fleece Knauf ecose: 7€
Vapor barrier Tyvek: 3€ (inside and outside)
Wood fiber insulation board: 8€ (inside and outside)
Plasterboard Knauf Diamant: 28€ (double inside and outside)
Putty, primer, paint: 4€ (only inside, plasterboard painted directly)
Wood facade larch rhombus: 20€ (with battens and additional vapor barrier)
Hardware estimated: 20€

Total: 103€/m²

The roof will be different but overall similar.
For the roof, I estimate 110€/m².

The floor should also be the slab.
Without screed, but insulated. I have already thought about
a Swedish slab, but I am not sure yet.
According to "Internet" the m² floor slab with insulation costs about 100€/m²
at 25 cm, although I estimate 7000€ for the floor slab due to own work.

Windows & doors: 4000€
Interior drywall with primer and paint (15€/m²) x 180m²: 2700€
Installation gas, water, electricity with heating system: 10000€
Machine costs, insurance, etc.: 2500€

So the materials for the house:
57100€

The grid connection should cost about 7000€.
The structural engineer is in the family.
I would like to avoid an architect,
if possible. Purchase incidental costs 10000€.

That makes 74100€

I have definitely forgotten quite a few things,
but they should be covered with the remaining 25000€.
I will use labor from my family.
The floor plan will be very reduced and open.
The ceiling height results from a mezzanine and gallery.

What do you think? Too naive? Forgotten too much?
Why is the house so cheap in my calculation?
Suggestions for improvement?

Most of it is already pretty ridiculous, but this item here

Windows & Doors: 4000€

tops everything.

I'm going to get some beer and chips.

Building permit with plan
Electrical installation

And when do you want to complete those few thousand working hours?

Hopefully the other numbers are better rolled. Windows and doors do not fit

I am open to criticism, but why should that be unrealistic? I ask for constructive criticism. I cannot post links here, but I found plastic windows with triple glazing 1x1m for 104€. I don't really expect to have more than 20 windows. Even if you add the costs for screws, sealing tape, etc., I still won't exceed 4000€ with the door, although I have to say that I am a journeyman in a woodworking profession and can do a lot myself.

Building permit with plan
Electrical installation

And when do you want to complete the few thousand hours of work?

Hopefully the other numbers are rolled better. Windows and doors don't fit

I am fortunate to have a large family and a job that I only have to do 2 days a week. Therefore, I have 5 days a week for the construction. Although I do not want to rule out getting helpers.