A rooflight can be positioned for the desk. Because it sits in the slope, we can place it above and slightly in front of where you sit, so that daylight falls across the surface from above and a little behind your screen. That avoids the glare you can get from a window on the wall behind or beside a monitor.
Height of the sill in a sloping room also matters. A VELUX roof window is normally set so that the bottom of the glass is within reach and the top gives headroom. In an attic room, this means choosing the position in the slope that suits a person seated and a person standing, and we can mark both heights on the wall during the survey.
Sun is the counterweight. A rooflight facing south collects the strongest light and the most heat. A blind, a solar control coating or a position on a north-facing slope all help to manage it, and each is a decision to make before the quote, not after.
The desk also decides how big the opening should be. A small unit over a small desk gives a neat patch of light but leaves the rest of the room dim, and a large unit over a loft floor can warm the room more than you want in July. We usually talk through two sizes at the survey, mark each one on the slope from inside, and let you stand under the line before choosing. It is easier to judge from the floor than from a drawing.
If two people share the room, the position changes again. A desk against each side of the room wants the light central, and a rooflight on the ridge side of the slope serves both. A single desk can sit nearer the opening and take the light from one shoulder.
A desk needs even light over hours, which is a different brief from a landing.