I would like to leave out the instructive part and think that your question from the original post has been answered accordingly.
Hi we have a house under construction in Baden-Württemberg where two parking spaces are planned, but I would like to put a garden house on one and fence it together with the garden, does anyone check that after construction? Or is one parking space enough in Baden-Württemberg?
1) The requirement from the development plan of your building area counts – if it states two parking spaces, then these two parking spaces must be created. Whether they are located somewhere on the driveway or in a garage does not initially matter. However, one must be careful here, "conflicted parking spaces" (for example, in front of the garage entrance so that one always has to move) do not count everywhere as a valid parking space to my knowledge. Here you would have to look specifically into the state building code and the requirements of the development plan.
2) If there is no development plan, then §34 in connection with the state building code applies. Assuming a single-family house, then one parking space per dwelling is required.
Generally, an exception can be applied for if the provision on your property is unreasonable or impossible for structural reasons. However, that would be an individual case decision and must be approved by deviation.
As for the question of whether it is checked or not, no reliable answer can be given and it depends in my view on your municipality. I have heard stories that after 2 years someone from the municipality walked through the new building area, looked at the houses and noted deviations.
You are only on the safe side if you build according to the requirements of the development plan or the state building code. It only takes one neighbor to complain about the parked car on the street and report you to the municipality. If they then realize that you did not build according to the building application, in the worst case this can mean a reconstruction of your garden or a fine.
If you definitely want to build one parking space less, then have it approved by deviation. If the building authority does not agree, then unfortunately you are out of luck.
I would also be interested in the floor plan. Would you like to post your plan here sometime?