what are the dimensions of the timbers, and their spacing?
Are you in Scotland?
Is it a house or bungalow?
What is on the other side of that plasterboarded wall?
please show us the outside, including the whole of the roof.
It may have been built with the intention of constructing habitable rooms in the loft. There may be insulation concealed behind the roof lining.
It's OSB, not ply.
Strangely, the electrician has run the cables where they will be trampled and damaged by the builder' boots, or any boards laid on top.