Build a terraced end house with an additional unit (GÜ) on your own

And those who plan and approve that live in the single-family house with 2,000sqm of land ^^

Thus, both are only allowed to build 6x12m including the terrace.

That just can't be.

Old Swede. There were tons of interns at work. Hochkantwohnung fits exactly right there.

This is more than intense. The persons in charge / responsible here should quickly make way...

It is intended that way. Double the number of taxpayers on the same area.

When you see the height, I find it hard to imagine filling up the plot. What happens to the excavation from the Viebrockhaus? Does he distribute it?

since they are not a middle house, the lower floor area ratio of 0.4 instead of 0.5 applies. Thus, both may only build 6x12m including the terrace.

6x12 m may be correct but whether the terrace is included is not certain – either the development plan allows something extra or one can present a "significant impediment to the appropriate use of the property" as an objection to the authority.

Building Use Ordinance
§ 19
Floor Area Ratio, permissible floor area

(1) The floor area ratio indicates how many square meters of floor area per square meter of plot area according to paragraph 3 are permissible.

(2) Permissible floor area is the proportion of the building plot calculated according to paragraph 1 that may be covered by buildings.

(3) For the determination of the permissible floor area, the area of the building plot located in the building land and behind the road boundary line specified in the development plan is decisive. If no road boundary line is specified, the area of the building plot behind the actual road boundary or the one specified in the development plan as decisive for the determination of the permissible floor area is decisive.

(4) When determining the floor area, the floor areas of
1. garages and parking spaces with their access roads,
2. ancillary facilities within the meaning of § 14,
3. building structures below the ground surface that only underpin the building plot,

are to be included. The permissible floor area may be exceeded by up to 50 percent through the floor areas of the installations referred to in sentence 1, but not exceeding a floor area ratio of 0.8; further minor exceedances may be permitted. In the development plan, provisions deviating from sentence 2 may be made. As far as the development plan does not specify otherwise, deviation from the compliance with the limits resulting from sentence 2 may be allowed in individual cases
1. for exceedances with minor impacts on the natural functions of the soil or
2. if compliance with the limits would lead to a significant impediment to the appropriate use of the property.