Revisions log for Answer #2385

It would be hard to get something really dark.

I would consider a blackout roller blind that you attach to the bottom edge of the window and cut into a triangle at the top. The direction of movement is from bottom to top, like triangular roller shutters.

But it's not very pretty, and there's always some light shining through at the edges.

If your partner really wants it to be dark, you will either have to pay $3,500 for roller shutters or change the dormer window to a rectangular window.