A roof window above and slightly in front of the desk fixes that. Daylight from overhead has no glare on the screen when it arrives from above and behind the monitor, and it reaches the whole surface rather than one edge. We work out the position by sitting in your chair, or standing where the chair will be, and looking up.
In a house with a converted loft, the slope often runs down to a low knee wall. That limits where a desk can go, and the rooflight is chosen to match. A unit set lower in the slope lets you see out when seated. One set higher floods the room with sky but gives no view. Both are reasonable choices, and which suits you depends on how you work.
If the room is a standard bedroom under a roof with a loft above it, the opening is cut through the ceiling and a short shaft is formed. That is a different job from a converted room, and the quote spells out which one applies.
Cables and sockets deserve a thought too. A desk usually has a tangle of leads behind it, and the shaft from a new rooflight should not run through the same run of timber that carries the wiring for the room below. The loft visit shows where cables and any pipework run, and the position is shifted clear of them.
Heat is the last thing to weigh. A study under a roof can get warm in summer with a computer running all day. A blind on the rooflight and a unit that opens will keep the room comfortable without an extra fan.
Overhead light reaches the whole desk instead of one edge.