As well as their standard flashings for pitched roof windows, VELUX offer a range of different flashings such as the recessed flashings like EDN 2000 suitable for slate.
There's also a huge range of twin and combination flashings, to cope with the demand of windows sitting side by side, even possible to have a Quattro flashing kit for up to 4 windows.

VELUX EDJ 0000 Recessed 90mm Profile Tile Flashing
From £70.56ex vat

VELUX EDN 0000 Recessed Slate Flashing
From £68.04ex vat

VELUX EDJ 2000 Insulated Recessed 90mm Profile Tile Flashing
From £112.56ex vat

VELUX EDN 2000 Insulated Recessed Slate Flashing
From £108.54ex vat