Insulate ceiling/floor - upper floor/cold roof

Hello everyone,
We have put up a new roof frame! For cost and demand reasons, the roof frame is to remain unheated for the time being (at least 10 years)! The gables will only be clad with larch. We want to insulate the ceiling of the upper floor or the floor of the roof with Isofloc/Thermofloc for thermal insulation. The following structure is planned (from top to bottom):

[*]OSB board 2.0 cm
[*]Isofloc 20cm between the ceiling joists
[*]"vapor-permeable" vapor barrier (tacked to the underside of the ceiling joists)
[*]chipboard 1.5 cm floating
[*]woodchip wallpaper

Does this make sense? Under what conditions could the vapor barrier (possibly punched instead of OSB) be omitted?
Is there perhaps an alternative, more cost-effective structure?
Later, the floor is to be converted (roof slope insulation, impact sound insulation above the OSB, etc.). Our priority is: long-term without building damage, as ecological as possible in DIY work, with low costs!
Thanks in advance, bemmel

Anyone who carries out such projects without prior professional planning should not be surprised by later construction defects.

And these are certainly inevitable with the approach presented here!

Sorry, but such planning is hardly feasible in a forum like this.

3. e.g. PE vapor barrier between 4. and 5. Battens GK Wallpaper LG

The described structural design is in no way capable of addressing the water vapor problem (both convection and diffusion).

Without professional planning, the commendable carpentry work is truly a shame.