yeah thats what I was thinking of.If you go for a glass/see through roof that's not going to allow walking on it - how about putting some joists just above it screwed into the walls with the occasional scaffold bar across them so you can put planks on when you need maintenance access?
SK10 Velux would be 114cmx160cm and you could take the sash out to gain access to your main roof.
114cm wide? The passage is 130cm wide so that leaves 16cm (8cm each side).
Is that too narrow consider the window-to-roof and roof-to-wall flashing? Also there would be the timber-work for the roof to consider.
I can't even begin to imagine the pain and suffering trying to fit such a large heavy Velux into such a confined space.
Bonkers.