For my many sins it’s finally time to come back and address this light well . Let’s get the laughter out the way - yes it will have walk on glazing .
As you can see it’s concrete with some PIR at the top . The concrete shuttering warped during the pour so it’s not level ( 2nd one is much worse - but that’s a problem for another day ) .
How best to line / prepare - possibly for tiling . Roofers batten vertically ( to get over the bow ) then tile backer board ??