Build a sheet metal hall on the border

Please excuse me, I was expecting such an answer. But that was not my question... I would like to ask you to answer only my question. I know about illegal construction myself and do not need the previous comment

You are a great guy.

If it is an illegal construction, the question of whether you are allowed to build is pointless. You are not allowed. End of story.

At most, your question makes sense in terms of an actual approval possibility, i.e., whether you can legalize the illegal construction afterwards if it is discovered.

For that, you definitely need to consult an architect who will examine the situation on site. In NRW you would probably encounter problems with the construction—whether with or without a pitched roof—regarding the following points:

1. Building window
2. Type of use?
3. Length of boundary construction (=> building encumbrance, mandatory)
4. Height/roof pitch
5. Openings on the boundary
6. Possibly access routes
7. ...

And these are only the points I deal with daily as a surveyor. Fire protection, structural calculation etc. are additional.

Regulations in NDS differ partially, but basically the same process applies. Moreover, the costs for a subsequent approval usually increase.

Best regards
Dirk Grafe

Hm, I understand the question from the OP "Am I allowed to build this?" referring to the new, planned hall with 4x4x8m and not to the old, current hall.

My answer referred to both constructions. The new building also requires approval due to its size and is an illegal construction without approval. Dirk Grafe also listed aspects that may potentially conflict with the project.

My answer already referred to both buildings.

That was not clear to me from reading your post.