Load bearing calc

[audi321]

Hi all, just wondered if anyone knew of a 'back of a fag packet' way to work something out quickly.

Roof trusses and tiles onto a single skin garage wall, nothing else........just seeing if I'll get away with thermalite blocks (3.6N/mm2) or dense ones (7N/mm2).

I know when the drawing are done it will all be spec'd out, but I'm in the very early 'in my head' stage, so just was wondering.

[bobtail4x4]

the trusses sit on a wallplate to spread the load,

garages have been built like this for years,
however thermalite is overkill in a garage,