Thank you for your fast response. I am not at home at the moment but the roof tiles look like these ones you can see on the picture attached. Yes, I got now a non opening rooflight, it is just like a rectangular window and I cannot even clean it from the outside. That's true that the roof is not flat. It is more like a hipped roof but the slope is not too steep. Yes, my idea is to change it for a roof light with opening panes or at least, if it is not possible for an opening one. Thank you for your help.