Jaques d'Alltrades wrote:

If you put up a ½m × ½m platform with a lip of something like 1" × 1½"
(sorry to mix systems) and they do get in, they'll like that, especially
if it's near the peak on a gable-end.

We've got the scaffolding until next monday so that we can touch up the
windows this week end. Ta for the advice but I won't go upthere myself.
I had a funny turn on the scaffold. Half way there my legs frozed and
my life flashed before me (

*SOME* light is necessary though: they are unlikely to nest in total darkness.

Ho! I guarantee light. My 15 years old alien is moving in the bigest
room. He can't switch lights off. But perhaps I could mention this to
the chap visiting us tomorrow evening. We need some repairs to the
gable and I don't want my husband to do it.