Offer for attic conversion - assessment?

Hello , thank you very much for the invoices. It helps a lot to check if we have forgotten anything etc. What exactly is meant by the ventilation, what is it needed for? There are already two large windows in the attic. Or am I misunderstanding the ventilation?

We have a central ventilation system (controlled residential ventilation). The newly expanded attic was also connected to it. If you do not have a ventilation system but ventilate "classically" through windows, it is not an issue for you.