Have you considered adding value through a roof terrace? It may be easier to integrate than you think!
It may be possible to convert your attic knee wall into an exterior wall. This can allow you to transform what was empty roof cavity into high value roof terrace.
Perhaps you have a pitched roof meeting a flat roof? In this case the adjoining flat roof can create additional property value if transformed to terrace space.
A terrace roof window system provides easy access to external space without requiring a traditional full height door. The height is instead achieved through a combination of a top hung window within the sloped roof, and a right or left hinged vertical panel below.