I’m not sure of the older type houses,but we as a rule lay 150mm below damp course,10mm from wall as your muck(mortar)joint will butt up against house,shingle as jag61 has said for aesthetics,remember as long as you’ve got fall No water will penetrate there as the muck will stop any ingress,be liberal with your fall,I’m guessing from window to left of door too gully pot is roughly 3.5m so yr fall wants to be minimum50/60mm,as said above there’s lots of different types of traps/lids/covers for yr downpipe outlet,remember yr falling away from the house.
Wright’s,what I mean too say is run from far window down too gully then off of slab,from the left side I’d fall from wall in same direction away from house,so basically looking at pic 1,window being north,run everything south,(mm,does that make much sense??)