Exception from the development plan for a carport?

The following applies to Lower Saxony:

In most municipalities and cities, carports are exempt from approval if they comply with the following rules:

[*]Floor area up to 30 square meters and a maximum average wall height of 3 meters
[*]the length is at least 5 meters.
[*]In the case of border construction, the carport may stand a maximum of 9 meters on one border and 15 meters on all borders.
[*]The width is set at 2.5 meters, for carports with one side wall 2.4 meters
[*]There must be 3 meters between the carport and the street.
[*]Construction is only permitted directly on the property boundary and within one meter of the boundary if the parking area is smaller than 36 m². The length may not exceed 9 meters. The carport may not be taller than 3 meters at its highest point.

However, if you want to build larger, then the full program with permits etc. applies.

For carports requiring approval, you usually have to submit the following documents. In case of doubt, ask the building authority of your municipality or city.

[*]Static calculations
[*]Construction description
[*]Construction drawings from three views
[*]The estimated costs for the construction
[*]A simple site plan with overview map
[*]The carefully and completely filled out construction application, available at the municipality, building authority or online
[*]The construction project must comply with the development plan

So with a normal carport of, for example, 4 x 7 m, there should be no problems and you can simply set it up anywhere.

No. He explicitly wants to build closer than 3m to the street, and therefore it is no longer exempt from approval.

In a boundary development, the carport may be a maximum of 9 meters on one boundary and 15 meters on all boundaries.

This is exempt from approval. So he can build on the boundary.

We did it this way with 9m on the boundary and then clad the side facing the neighbor with wood. The building authority objected to this because the gable end of the neighbor's house is only 3m away there and, for fire protection reasons, a non-combustible wall was required. I no longer have the legal details of the criticized matter exactly in mind and only want to say that this should possibly be clarified in advance if a similar situation/proximity to the neighbor's house exists and the side wall is to be clad.

This is exempt from approval. So he can build on the boundary.

Read your own post about Lower Saxony and carports. 3 m distance to the street.

If you can ever upload a plan?

As described in the other post, I think that can work.

How big should it be?