Tips for a sports shed or garage?

Good evening,

we would like to build (or have built) a larger shed/garage on the left side of our house in Brandenburg. The distance from our house wall to the neighbor's property is 3.50 meters. We are only allowed to seal 18m2 more. In Brandenburg, a shed over 75m3 requires a permit.
Therefore, we plan to build a 2.50 x 7m shed/garage. We want to use it exclusively for exercising, i.e., we want to store sports equipment and weights in it.
Our goal is to build something stable as efficiently as possible, that is low-maintenance and does not need to be painted every year.
We do not need a shower inside, but possibly heating, as we want to exercise 2-3 times a week throughout the year if possible. Currently, we only have a suitable outdoor electrical cable, which we would use for a socket column to keep costs low.

Now to the question:
Can you recommend materials? Solid construction with stone on stone would cost us about 30,000 EUR, which is too much for us. A wooden shed variant would probably cost about 6,000 EUR in materials.
Have you perhaps realized similar wishes? Can you advise against anything or do you have helpful tips that we should consider?

What you are planning ([Sportraum zur mehrmaligen wöchentlichen Benutzung (wenn auch nur saisonal)]), is called a common room and may not be built within the boundary distance to the property line.

hardware store shed wood cost me 900 € and I built it myself with a friend

HelpHelp do you have a photo at hand? :) Actually also as a kind of sports room - if yes, do you heat?

@ ypg: BBgBO § 2 Terms: "Living rooms are rooms that are intended or suitable for the not merely temporary stay of people." 2-3 times per week for 1 hour are still "merely temporary," especially if a lawn mower, bicycles, and tools are also stored there, or do you have a more specific definition?

The legal side could become difficult, but I am deeply involved to say something precise.

Now about the room itself. If you subtract the walls from the 2.5m width, it becomes quite a narrow tube. Additionally, you should also consider the height. What height is necessary for your sport?

If I understand correctly, you only want to heat the room shortly before training. In winter, the short or long barbell will still be an icicle despite the warm room. Are electrical training devices like a treadmill planned? For those, I find large temperature fluctuations not optimal. Furthermore, in such a pain cave there is often a TV hanging and internet is also quite useful.

Don’t forget to be able to ventilate the room well.

Have you perhaps already put similar wishes into practice?

See here:

2-3 times per week for 1 hour are still "only temporary"

From three minutes on, stopping becomes parking, even if the driver does not get out.