Brydo Is there any reason ou want to paint your roof?
Everbuilds Black brush on bitumem based with added fibres for added adhesion, is for tiles etc. I paint the pack of my garage where damp can get in with it and it sticks like you know what and lasts.
I think Johnstones do a paint for bricks, tiles etc Think its called step paint but, no idea on lonetivity.
Make sure you remove all the moss and lichen prior to painting.