Construction of a double garage

Hello house building forum colleagues,

at my brother's place we want to build a double garage as a DIY project.
So far so good... until the topic of the roof!

The garage has a size of 9m long and 7m wide (external dimensions)...
The idea is a cost-effective wooden beam ceiling... and that along the length (for "aesthetic reasons")

could someone help with the dimensioning of the ceiling (beams)?
The walls would be built from 17.5 Poroton bricks and have a ring beam all around.

Thanks and regards
Alex

oops wrong thread... can someone move this to [Ideenfindung]...

You need a structural engineer for that anyway. In that respect, he can also properly calculate the required dimensions of the beams for you. Any other answer would be more than negligent due to the lack of further details.