Could you post a drawing, 9’ seems like a very deep dormer.

Photo? A 5' X 9' space is a junior bowling alley...

What is the alternative? Dormer or no dormer? What is the space that the dormer is in and will it benefit from a window? If you just want light, would skylights work?

My daughter has two such dormers in her house, one in each of the two front bedrooms. In MBR, it's used as a sitting area - club chair with ottoman and table with TV. DD loves it - it's her retreat. The other is in the boy's BR. DGS1 has his twin bed in it, crossways under the window. He also has a long ramble/console. It gives him some separation from his brother and vs versa. It works.

Thanks for the responses so far. The room is a small upstairs study that will have an incredoble view if we can get through the roofline-hence the dormer idea. We are trying to make it wider but if we can't we need to decide whether to do the dormer or not.

Have you considered a wide shed-type former, rather than a narrow gable-style?