ᐅ Construction of a Double Garage

Hello house-building forum members,

My brother and I are planning to build a double garage ourselves.
So far, everything is fine... until we get to the roof!

The garage measures 9 meters long and 7 meters wide (external dimensions).
The idea is to have an economical wooden beam ceiling, oriented lengthwise (for aesthetic reasons).

Could someone help with sizing the ceiling beams?
The walls will be built with 17.5 cm (7 inch) Poroton bricks and have a ring beam all around.

Thanks and best regards,
Alex

Oops, wrong thread... Can someone move this to the idea brainstorming section...?

You will need a structural engineer for that anyway. They can properly calculate the required dimensions for the beams. Any other answer would be reckless without more details.