On Monday, 11 May 2020 22:01:21 UTC+1, wrote:
If the cladding was flat it would make sense to: frame and skin, then
cut openings, then add vertical reinforcing timbers to take the weight
of the windows and then fit the windows and glaze - simples! However,
the cladding is not flat and I can't get my head around how to cut and
trim it so I can inset the windows. There must be an easy solution but
it eludes me thus far.

This is a discussion of fitting Velux windows in corrugated tin.

https://forum.buildhub.org.uk/topic/...metal-roofing/

Owain