Pitched roof construction, how...?

HELLO, after 8 years of absence!

I am currently planning a small outbuilding (not a permanent living area!), which is to have a green shed roof, constructed using a wooden structure.
Now I unfortunately realized that I cannot find a "proper" solution for the structure, or I can't decide:
1st idea = classic structure
-> supposedly completely outdated and severe problems if the vapor barrier is defective.
2nd idea = ventilated from behind
-> somewhat worse insulation value, but a possibly defective vapor barrier would not be so dramatic!
3rd idea = insulation above rafters
-> better storage capacity, but quite a high build-up and probably the most expensive construction.

Do you have any thoughts on the ideas, or should I consider something completely different?

How should the roof pitch be?
How will the building be used?

I strongly recommend version 2 or 3.
For version 2, increase the ventilation cross-section; the flatter the pitch, the larger it should be to ensure there is still a real airflow afterwards (e.g., at 10° at least 80mm).
For version 3, execute the vapor barrier as a bitumen membrane, e.g., Bauder Tec.

So the building is supposed to be a kind of mini summer holiday house.

The roof pitch must be under 15°, which I probably do not want to fully utilize, as I still have to think about the aesthetics, as well as the height clearance.

But thank you very much for the tip about ventilation, that was unknown to me!

By Bauder vapor barrier, do you mean use under the gravel / earth floor? Actually, I had thought of bitumen membrane + 1.5mm foil on top (not shown), but I am not 100% convinced about the long-term tightness of the bitumen membrane.

Best regards René

Idea 1 any further disadvantages, as already mentioned by me?

Hi

I would also choose option two and replace the [Unterspannbahn] with a [DWD-Platte] as well as the [OSB-Platte] with [Schalung].

Olli

Dwd panels are completely new to me, I will inquire about them next week.

Prefer formwork, because of conviction or moisture susceptibility of the ob-panels?