Restrictive development plan - is buying land worth it?

I don’t think so. It must definitely be plot ratio.

I don’t think so. That would mean a municipal statute overriding federal law.

I have attached the regulation from the development plan so you can get an idea for yourself. I’ll try to upload the entire development plan later, but I read in other threads here that PDFs are not accepted as attachments...

The development plan is from August 2016; before that, the area was apparently only used for weekend houses. The plots are also more or less "in the middle of the forest," and the plot that was offered to me is currently still completely full of trees. This might be the reason for the restrictions. I haven’t found the justification for the development plan yet; I have to inquire at the city. I don’t have the site plan with elevations yet, but it is relatively flat, slightly sloping towards the southwest.

With a basement, you could achieve something:
Have the basement protrude as far as allowed by the ridge height and the definition for (non-)full floors. Then a ground floor as a full floor and an attic floor on top. If you want, and as long as the development plan allows it in terms of roof shape, you could work with a flat roof section in the middle and pitched roof areas on the sides—again designed so that the definition for a full floor is just barely not exceeded.

That sounds interesting—but since that would not be a pure storage basement but rather a living basement, it probably wouldn’t be really cheap either...

Is there actually a rough guideline for how much percent of the base area ultimately remains as living space? Of course, I understand that it always depends on how thick the walls are and how many there are (in addition to the exterior walls), but a rough guideline or a range from/to would at least help me for starters.

As I understand the excerpt, you are allowed to build a total of 110m² on the property. Including all ancillary facilities. In this respect, the property is unsuitable for your project.

As far as I understand the excerpt, you are allowed to build a TOTAL of 110m² on the property. Including all ancillary facilities. Therefore, the property is unsuitable for your project.

Yes, the floor area ratio of 0.1 probably doesn't allow for more.

Are you sure about that? I read it simply like this:

2.1 Residential buildings have a floor area ratio of 0.1, but a maximum floor area of 110 sqm (i.e., for plots larger than 1,100 sqm, the floor area may also only be 110 sqm, even though the floor area ratio would allow more, e.g., for a 1,500 sqm plot floor area ratio 0.1 = 150 sqm). The floor area of the house is floor area I.

2.2 Floor area II (driveways, terraces, etc.) may exceed floor area I by up to 100%. The term "feasible building floor area depending on the permissible floor area ratio" is, in my view, only relevant for plots smaller than 1,100 sqm, e.g., for a 900 sqm plot the feasible building floor area is only 90 sqm, therefore floor area II may exceed this 90 sqm by up to 100%.

Due to the regulation in 2.4, even more than 100% is possible in the result, depending on the material used, since for example access paths with paving and joints > 15% are only counted as 60%.

I have attached the regulation from the development plan

Well, once again the professionals were at work. Apart from the fact that I do not see the regulations as being covered by the Federal Land Utilization Ordinance (but lawyers should take a closer look at that), "floor area ratio (base area I)" is definitely wrong, since floor area ratio means floor area ratio, thus has nothing to do with driveways, etc., and it is also a ratio and not an area. Whatever the urban planners wanted to regulate there, the formulations have gone terribly wrong. But since people are reluctant to argue with the approval authority, especially legally, you will probably have to ask on site what is possible.

Well, once again there were professionals at work. Apart from the fact that I do not see the regulations covered by the Baunutzungsverordnung (but lawyers would have to take a closer look at that), "Geschossflächenzahl (Grundfläche I)" is definitely wrong, since Geschossflächenzahl means Floor Area Ratio, so it has nothing to do with driveways etc., and it is also a ratio number and not an area.

Whatever the urban planners wanted to regulate there, the formulations have gone terribly wrong. But since one is reluctant to argue with the approval authority, especially legally, you will probably have to ask on site what is possible.

I agree with you, this is all unnecessarily complicated. But which regulation exactly do you think violates the Baunutzungsverordnung (so that I know which points I should specifically inquire about with the approval authority)? The floor area is regulated in § 20, and according to that, "ancillary facilities within the meaning of § 14, balconies, loggias, terraces, as well as structural facilities, insofar as they are permissible or can be permitted under state law in the distance areas (lateral boundary distance and other distance areas)," are excluded from the calculation of floor area. I understand this to mean that in the end only the ground floor area (as the only full floor) counts as floor area?!