Before it slopes center it........., OR if you want to lay in bed and look out.....within a foot or 2 of the beginning of the slope, --------or, if you just want it for daylight, not to look out of, maybe within one or 2 feet of the opposite side of the wall from where the slope begins. I do not like windows in the exact corner of bedrooms if they are, like 3 feet wide... I always figure I want to be able to put a dresser or a desk in that corner, and I want the chair that goes with it to be centered in the window if someone is sitting on it(not if it is pushed under the desk). I think a bedroom looks nicer if there is a dresser or a desk against a right angle wall to the window and not seen from the outside of the house. People look out windows, so you don't want to have to put furniture in front of it, if the window is the width of the ** side view** of the furniture item(2 or 3 feet total width and similar depth to that dresser, chest, or desk...Similarly, don't put the headboard at a right angle to a window wall...See in the picture, the night stand is in the corner. The window begins AFTER the night stand, a couple of feet from the corner of the wall. It just looks nicer that way...