The Owlery is the room in which all the student's owls sleep while they are attending Hogwarts School.
From the Story
Discovered in Book 4, Chapter 15, Beauxbatons and Durmstrang
"The Owlery is a circular stone room located at the top of the West Tower. It is a cold, draughty room as none of the windows have glass in them. The floor is covered in straw, owl droppings and regurgitated skeletons of mice and voles.