In message , Harry Bloomfield
writes
Tim Lamb presented the following explanation :
Building control are stressing about the lack of a protected exit
from a bedroom in the chalet bungalow.

One way out:-) would be a top hung roof light. Marley concrete tiles.

Anyone done one? Any reasons why it needs a professional roofer?

I put a centre hinged one in 30 years ago. It took a lot of courage to
cut the hole, but it was much easier than I anticipated. The roof
timbers will need proper support where they need to be cut and the
cross timbers properly fixed.

These are timber trusses but I'm hoping the spacing will be OK as I am
simply fitting a second light lower down the roof.

I spent days rehearsing the exercise and chose a very dry day, just in
case, but still failed to properly check the supplied flashing in the
kit was enough, so had to ask Velux to deliver extra urgently and hope
it didn't rain until finished. I was lucky.

The Velux site offers matching flashing kits. Presumably your roof
tiles/rafter spacing were unusual in some way.

--
Tim Lamb