Living on your own land as you wish?

So if I have a house designed (by the architect) etc. that is solid and declared as a residential building - and submit it to the building authority - there shouldn't be any problems?

Hello Magico,

there are various points that must be considered, but all of these must be viewed under one decisive point:

in BB, a building permit is required from 75m³ (cubic meters) of enclosed space, regardless of whether it is a house or a garden shed. With 50m² of living space, you are definitely in the area requiring a building permit, in which case all other legal regulations will be checked.

Source: Landesbauordnung BB, §55 (2) ff

So if I have a house designed (by an architect) etc. that is solid and declared as a residential building - and submit it to the building authority - there should be no problems?

The new building must at least be within the building envelope or (if no development plan is available) adapt to the existing residential buildings.

Best regards
Dirk Grafe

Can and may are not the same.
Even a garden shed must be approved. Either by exemption in the development plan, or by application to the responsible authority.
In Germany, not everyone may simply put houses of any size on their property. When applying for a building permit, evidence of structural stability must be provided to prove that your house will not collapse.
Go to your local building authority and ask what you are allowed to build on your property. And: Even if the neighbors have unauthorized buildings ([Schwarzbauten]), you are not allowed to do the same on your property in return.