What is allowed on private green spaces?

It is possible that a private green area is prescribed behind your house as part of the [B-Plan]. Also in the inner area. From a building law perspective, it will be easier to construct a small outbuilding there. But it is not planned there.

You will have to inquire at the building authority. I do not have a reliable answer for that either.

Do you have to pay the price for the entire area, even though only part of it is usable, as if it were all building land?

Yes, it looks like we will have to pay the full price. Unfortunately, the plot is insanely expensive (650€ per sqm). We could try to negotiate further with the seller, but then it might go to another buyer. And we definitely want to have it. That’s why we will probably just pay the price.

Just post an aerial photo with the surroundings. You can clearly see what the neighbors have done in the green area.

Designating it as a garden already means that nothing is supposed to be built there. But a garden shed in the size of 2*3m should, in my opinion, not be a problem.

Do you have to pay the price as if the entire area were building land, even though only part of it can be used?

That's always the case with a development plan. You are only allowed to build within the building line. But you pay the price for the land that is asked. How the green spaces are to be designed is often prescribed quite precisely.

The one sentence that showed here is rather unusually brief.

Whether one should even buy such properties in the current situation? Personally, I would refrain from it. You pay a lot of money for a plot of land and cannot use it. Your question here implicitly shows that you yourself are not satisfied with this condition.

I pay the price for building land and the green land price for green land.

Here with me there is currently a building plot for sale. 1300 sqm, fully developed with a demolition house and barn for sale. Here you can still partially use something. Electricity, water, telephone, etc., are connected and can be used immediately. The plot is square-shaped and flat. The seller wants 29,900 euros. [VHB].

So whether I would tie such a burden to myself in Hamburg, I don't know.

Thank you for all the answers. It is important to us that a small tool shed and a playhouse can be placed on the area and that it can be enclosed with a fence. The property borders a pond (there are still 5m from the property boundary to the shore) and we have small children. Therefore, an enclosure by a hedge would not be sufficient. Unfortunately, the development plan for the area ends at the property boundary. I can therefore not see what the plan foresees for the neighboring properties. I think I will call the building authority tomorrow. The price is steep, that’s true. However, other plots here are not cheaper and we would also want to use the green area on another property mainly for playing for the children and gardening. Hopefully, this will be possible on the private green area of this property.