House from the 1930s. Renovate or rebuild?

TeamMassiv: Here I would consider doing the electrical work together with an electrician (family) myself. Regarding radiators, I thought you can't really go wrong... I would find a tiled stove great for the new build. That probably adds another 10,000 to the bill. I don't have huge demands for tiles. But even better ones (calculated at 20 Euro/sqm) should now maybe cost only 2,000 Euros more? A nicer shower would also be appropriate.

Electrical work that is time-critical at this scale I would think carefully about; if you don’t install the cables in the ceiling on the day scheduled according to the construction timeline, you will delay all subsequent trades. For most general contractors, the 6-7 month construction period is fully scheduled. And the credit issued for doing all the electrical work yourself is often not that great. Probably difficult regarding warranty anyway.
Paving also costs money for the paving stones, gravel, etc.; although you save something, you still incur costs.

No one wants to talk you out of it, but inform yourselves well beforehand and always calculate with thick gloves.

What still slightly confuses me are the mere 10 windows on 180sqm...? Otherwise, I find the cost estimate for the renovation more realistic than the one for the new construction

House from the 30s doesn't sound so bad, more solid than from the immediate post-war period. Possibly still lead and cast pipes inside. Non-load-bearing interior walls often as Rabitz walls (ok). Presumably no asbestos, but possibly lindane in the wood (windows, ceiling paneling) from renovations in the 70s.

Regarding the basement, I'm not sure if I'm interpreting your description correctly. I would continue to use a low standing basement (200 cm, still over 180 cm after insulation) if dry, but not a crawl space basement (140 cm or less). Assuming a house connection and storage basement, without home office / guest room. Partial basements are often even more practical if you don't want to build the new house in the same dimensions. If the staircase location doesn't fit, possibly create an outside access and close it upstairs. One would have to explore on the specific plan what ideas come to mind.

I cannot imagine that a demolition would be worthwhile. Better sell and build new next door. At first I thought "Munich", okay, but in the north another plot should be found. Therefore my approach: renovation or sell.

So the basement (in my opinion dry) is between 1.80 to 2m and has its own entrance. It is not under the entire ground floor, but only a part of the ground floor.

Basement: 65sqm with 5 rooms – unheated

Ground floor 90sqm (this was extended in the 70s) with 4 rooms, hallway, bathroom, kitchen

The ground floor is about 1 meter above the ground (stairs).

Attic 43sqm with minimal roof slopes

And at the very top a small "crawl space"

Garage: directly attached to the ground floor – roof leaking – wall wet

Basically everything is from the 70s (renovation), only the solar system was installed in the 90s and the gas heating in 2015. The pipes are probably also from the 70s. I would probably have these replaced. Same goes for electricity, satellite system,...

I can't say much about it, but a proper conservatory for 8T€ is definitely not going to happen. For a decent (heated) conservatory, you quickly end up spending a total of 40-50T€. We had quotes for a patio roof. That was already in the range of 15-20T€. Additional glazing all around as a so-called summer garden would have been another 10T€ or so more.