You need 35° minimum for slate, and that drawing looks like about 15.
The box gutter will need a ply base going up the slope to make sure that no water runs back up and under the slates.
No cavity tray or DPC appears to have been specified at the parapet. I hope your builder is clued up about these
The box gutter will need a ply base going up the slope to make sure that no water runs back up and under the slates.
No cavity tray or DPC appears to have been specified at the parapet. I hope your builder is clued up about these