Massive house construction with a basement and a granny flat affordable with 340k financing?

A few points: a) I do think you have a chance of getting it financed b) Keller really seems to be too expensive c) Alternatively, you could plan so that the second floor could easily be converted into a separate apartment later c) would also be an option to generate rental income in case of unforeseen difficulties or when the children have moved out or for multi-generational living with the children

If 800 m2 of land with a value of 250 TE is available in a sought-after big city, then I would ask a general contractor (GU) if they have a building partner for a semi-detached house in reserve. 300 m2 for the partner quickly amount to 100 TE, and the project would then be jointly handled by a planner.

The 100 TE would probably be the equity you still need for an easy financing. But then you only have 500 m2 left. That should still be more than for a detached house (REH). Or instead of a semi-detached house (DH), maybe two city villas with 400 m2 each would be possible.

Would the development plan allow that? What does the building authority say?