Flat roof garden house roof construction

Hello everyone,

this year we want to tackle the garden house. It is to be a masonry house.

I have planned the roof structure as follows: - Rafters (50-60 cm spacing between the rafters) - on top of that then 22mm OSB boards - and as a "finish" on top roofing felt / bitumen shingles or also trapezoidal sheet metal.

The house will not be heated and basically not insulated.

Does that make sense? I have some concerns regarding moisture issues. So on one hand condensation inside the house (OSB is rather tight, would tongue and groove perhaps be better??) And on the other hand, if it is trapezoidal sheet metal, how does that behave with moisture that gets between the sheet metal and the OSB? Does the OSB board possibly still need a kind of underlay membrane?

I am looking forward to your ideas :)

Thanks Greetings and have a good start to the week!

Hello everyone,

anyone have an opinion or idea on this?

Thank you!