WHY a corner FP at all? As for now where to put the stone IMO it looks off where it lines up with nothing so maybe post the drawing of the wall unit to give this some reason for where it ends now.

I might consider a large-scale tile for the face of this wall, but not any primitive texture stone.

I'd place something 3D on the face of the flat wall.

I think you might end up creating a big tall decorating problem for yourself. by taking it up to the ceiling, as you can see from the photos below. Keeping it at the level of the built-ins gives you more options -- including the option to integrate into the shelf design. Have you considered that?

This might be a stylish solution (obviously the angle going the other way to meet the top of the middle window)

Mid century modern meets Transitional design in La Canada Flintridge · More Info

It should go to the ceiling; otherwise it'll look too stubby.

Wherever it goes, what will you do with the left side corner above where the bookshelf ends? In other words,since the side of the fireplace on the left will only be flush with the shelves to the top of the shelves, what will you do above that if you take it to the ceiling? Do you understand what I’m getting at?

debra

Debra - I get it! Good question.(Took me a bit.) I think the high left side of the fireplace would have the same stone as the front.

Beverly and mytwo cents - thank you so much for the pictures! We have decided to for sure go to the ceiling. Partly because we don't want the wall of windows to take over the living room. We want the fireplace to be just as important. I will post a finished picture when we're done.