Single-family house feasibility / provider selection

we did not accept the offer, but now have another offer for a building plot for a semi-detached house [...] This time without district heating network and without obligation to build according to QNG. A flat roof with extensive greening is mandatory. We are undecided whether we should try again here.

If the semi-detached building plots are available individually and the neighbor may choose a different planner and shell builder, then my tendency is clearly no. A semi-detached house with a flat roof will require II VG plus a recessed top floor.

The units are separate and construction with different companies is allowed. 2 VG are necessary, the stepped floor is optional.

The plots are individual and you are allowed to build with different companies.

That would be too risky for me, see Goalkeeper thread.

2 VG are necessary, the mansard floor is optional.

Legally yes, but the usual building proposals only work with a roughly 35° pitch attic, whose space here must come from somewhere equivalent.

I would have the soil survey done immediately. That helps to get more clarity for the earthworks in order to calculate them better. The offer contains some assumptions that are not clearly confirmed to be accurate.

We bought the plot. Our neighbors are building without a basement and without a top floor with normal ceiling height; additionally, we have the right of first refusal. After numerous discussions and offers, we decided to build with a general contractor because we want to calculate with a fixed price and place little value on individuality or flexibility. What do you think of the offer for 120 sqm flat roof, 2 full floors?

"A semi-detached house has TWO halves" (this is also the title of my external fundamental post). You don't have to build mirror clones, but you should – especially on the community side – pay attention to coordinating the house profiles. Building with one (i.e., joint) general contractor is very helpful in this regard – at least during the shell construction; after that, the awarding paths may gladly diverge. A shared planner is even more important. What is meant by the right of first refusal: an agreement on which neighbor starts? – and what is a "normal" ceiling height? If the neighbors want to be without a basement, you should do the same or you "have" to build first.