The shape of the table decides the layout. A round table for four needs one window centred above it. A long table for eight is better served by two windows in a line along the length, which spreads the light evenly instead of leaving the ends dim. A table pushed to one side wants the window offset in the same direction, so the glass is over the diners and not over the empty floor.
On the visit you are invited to take a seat at the table. We look up, find the closest gap between rafters that is wide enough, and check the height of the slope above your head. If the ceiling is sloping, a window that sits too low will be in the way when you stand. We settle the position with a tape and chalk on the plasterboard, so you can see exactly where the opening will fall before anything is cut, and move it if it looks wrong.
Chairs matter too. A table with a bench along one wall and chairs on the other sides has a lopsided centre of gravity, and the window belongs over where people actually sit, not over the geometric middle of the room. Homework spread across a table, a laptop propped on one end, a jigsaw laid out for a week are all reasons to want even light over the whole surface, not a bright patch in one spot.
The table below sets out a few common arrangements.
Light from above reaches every face around the table, which a side window cannot do.