How to properly cover the attic at Massa Haus Gmbh Simmern?

Hello, I live in a Massa Haus prefabricated house built in 1999. I plan to insulate the attic to create proper storage space. Currently, there is Rockwool insulation wool between the rafters and nothing else, so in the slopes and in the intermediate ceiling to the upper floor. At the moment, there are loose OSB boards lying around so you can move around a bit. Now I wanted to install vapor barrier foil over the insulation on the slopes and then OSB panels, also on the floor.

Can this be done like this or is there a risk of mold or something? Furthermore, there is a chimney in the attic and a chimney sweep hatch made of PVC glass, not insulated.

I hope someone can tell me something more precise about this, possibly also which foil is required.

Best regards, Ronny

Be sure to consult a professional. You have a cold roof, and there is surely a reason for that, so what you must absolutely not do is lay the OSB boards tightly together. Then the insulation wool will mold. If you want to lay a floor, then only tongue and groove boards. They are vapor permeable. And even then, do not lay them completely to the edge... there must be air underneath.

so leave space at the top and bottom and preferably leave space behind with battens...where or who is the expert for this? An architect?

best regards Ronny

what thickness should be used for the floor, isn't 23.5 mm a bit thick, you won't be putting any furniture on it.

best regards Ronny

Not at the top and bottom, but at the edge...

BUT I am not an expert, I am just repeating what my site manager told me and what seems logical to me. Every carpenter or drywall installer should know about this, otherwise just ask a building surveyor, architect, or site manager...

Tongue and groove boards are breathable, which means moisture can pass through. That is not the case with OSB.

Hardware stores mostly sell only 19mm stuff, that would be too little for me, I will install 22mm.

I got an offer from Leymann for 23.5 mm, they don't have anything else, it then costs about €10 per sqm. Quite expensive. I will do the sloped parts with drywall, with a vapor barrier behind it. I will leave the straight part at the top towards the ridges open, so any possible condensation can escape.
I don't think the 19 mm is sufficient, I wanted to screw counter battens on the valley beam anyway at a distance of about 30 cm...

Best regards, Ronny