Ha - you typed at the same time as me.you can use lead for the top and at the foot of the window
as goes for the sides can be done in either tin or lead
there really only trims to seal the sides of the roof
Actually... i have all the old lead from the chimney we rebuilt so could probably repurpose that for here. I was going to weigh it in but its just occurred to me that its probably re-useable for this project.