You can see a circular aperture at the bottom of the light well. This used to hold a circular window with glass in 8 frosted segments. There are marks in the surviving, almost complete, wooden frame every 45 degrees. Greg reported that the well was only rough plastered originally because, given the frosted glass, there would have been no need. My current thought is to use clear glass as the replacement for maximum light transmission and indeed to show off Greg's coloratura plasterwork.
When I visited Balthayock House nearby (a possible restoration candidate - now demolished) the light wells on the top (first) floor were egg shaped with circular openings on the roof, so you got a wonderful softly moulded sculptural lighting effect just from daylight alone. The light well as a art form.
In the photo below you can see the newly installed skylight in the roof, with new slating round the edge.
Patching up the roof is a slow business, but this step forwards was particularly welcome, given the leak in the entrance hall which has suddenly got a lot worse. With every step backwards, one needs a step forwards.