Is a brick tool shed exempt from approval?

That is the only thing I also thought, although I always thought that nothing is allowed outside the building zone, therefore very uncertain.

And regarding the federal states, the above is the excerpt from RLP, where I am also building.

What I have generally noticed so far, laws and sense? Hm ...

My garden shed with 12m² requires a building permit, but if I call it a garage, I can build 50m² monster halls without a permit. Can someone explain that to me?

Garden shed = building with living room(s)
Garage = building without living room

Higher standards are applied to buildings where people stay permanently. Even here, strangely enough, life/health of people is still prioritized over possible damage to cars — at least according to the state building codes.

The exterior area is not outside your building boundaries. The exterior area is defined in the land use plan. If you have a valid development plan, it states very detailed what you are allowed to build. You can read that yourself in the ordinance of the development plan. You don't always have to burden the administrations,...

Laube = building with living room(s) Garage = building without living room

Oh really? So if I build a shed (those wooden things), let's say to store hay and a lawnmower, I don't need a building permit, even if it is 20m²? But if I build exactly the same thing and put a table with chairs inside, I need a permit?

Oh really? So if I build a shed (those wooden things), let's say to store hay and a lawnmower, I don't need a building permit even if it is 20m²? If I build exactly the same thing and put a table with chairs inside, do I need a permit?

In BB it is formulated like this in the building code:

No building permit is required for the construction or alteration of the following buildings: Buildings without living quarters, toilets or fireplaces with no more than 75 m[SUP]3[/SUP] of enclosed space
...
above-ground garages with no more than one floor and no more than 150 m[SUP]2[/SUP] floor area ...

So if you build such a "wooden thing" and the part is not > 75 cbm, that would be permit-free in BB. If you then put a table and chairs inside to keep your lawnmower company, that should not matter to the building authority. It would matter, however, if curtains suddenly hang at the window near the lawnmower because you want to move in permanently and maybe also install a toilet. Then there might be living quarters, for which a permit is necessary.

This is because higher requirements apply to living quarters (light, room height, fire protection, escape route, etc.), see BB Building Code:

(1) Living quarters must have a floor area sufficient for their use and a clear height of at least 2.40 m. Living quarters in the attic must have this clear height over at least half of their floor area; room parts with a clear height below 1.50 m are not considered. For subsequent conversion of attic rooms, a clear height of 2.30 m is sufficient.
(2) Living quarters must be sufficiently illuminated and ventilated by daylight. The structural dimension of the lighting openings must be at least one eighth of the floor area of the room including the floor area of glazed extensions or loggias; the floor area of extensions that impair daylight illumination of the room must be included.
(3) Living quarters whose use prohibits daylight illumination are permissible without lighting openings. Living quarters without lighting openings must be sufficiently illuminated and ventilated by technical means.

You do not need to observe these regulations for the lawnmower.