Young landowner - build or rent?

You can still have kids at 35, theoretically even until shortly after 40. And now don't come at me with biology...

Otherwise, it simply depends on your life plan, no one here can help you further with that. We can only give you food for thought and explain why rent is not burning money and definitely has its justification.

Best regards

I also believe that the area of a semi-detached house on the ground floor is not necessarily sufficient for a complete residential unit. I would basically plan differently.

That also seems very likely necessary to me, because:

however, my parents wish for a roof terrace on the double garage

This wish can require quite a lot of plot width. Garages lose their boundary construction privilege if they have a terrace. At least on the boundary-near half there should be no terrace. And/or this garage would have to be moved to the side where the parents’ house currently is and registered on that property, requiring approval of this development.

Thanks for the tip about the boundary construction! I knew the garage was only allowed to be 9 m long, but I didn't realize that a roof terrace would change that!
So I guess that's it for the roof terrace on the garage, since the plot is only 15 m wide and 37 m long...

The suggestion of the flat-roof bungalow is definitely better! :)

The suggestion with the flat-roof bungalow is already better!

This is not allowed everywhere either. You can already post the plot dimensions and the information from the development plan here.

So the plot dimensions are exactly 15 x 37 m, there is no development plan, I have already specifically inquired about this at the building authority. It states a 5 m distance from the street (whereas the neighboring house has at most 3 m) and 3 m distance to the respective neighbor.... In our neighborhood, there is pretty much everything from bungalows to 2.5-storey buildings. Flat roofs, gable roofs, and Tuscan houses are also within sight.

It says 5 m distance to the street (whereas the neighboring house has at most 3 m)

How does the municipality justify this legally? Common practice is either a development plan (if the building area is still new) and then many specific regulations (roof pitch, number of residential units, floor area ratio and its exceedance for driveways, etc.) or §34 (integration into the existing environment = orientation to the neighbors, especially typical in village settings in "grown structures"), but then for example existing building corners are used as building line guidelines, however, not unequal treatment between old and new. What sometimes happens is that the respective state building code now prescribes distances between carports and public street space.