A robe is one of the few pieces of joinery where the brief is genuinely personal. Two people with identical rooms can need completely different insides, because one has forty shirts and the other has four coats and thirty pairs of shoes. So we ask what is actually going in there before we draw anything.
The ratio of long hanging to short hanging is the first decision, and most people overestimate how much long hanging they need. Short double hanging gives you twice the rail in the same width. After that it is drawers against open shelving. Drawers keep things out of the light and out of sight but cost more space; open shelves are cheaper and faster to use but only work if you are tidy. We usually end up with both, with the drawers where you reach naturally and the shelves above.
Then the details that make it feel finished. Shoe shelves pitched so the toes point up and you can see the pair. Pull-out trays for belts and watches. A mirror on the inside of a door rather than taking a wall. Lighting inside the robe, not just in the ceiling behind you, because a downlight in the middle of the room puts your own shadow over everything you are trying to look at.
