SFGate

Dytecture I would have the built-in the same height as the window so it is visually balanced.

Teresa Smith I agree with that. Match the size of the built -in to that of the window, with equal distance from the fireplace.

Dar Eckert Wrap bookcases around the corner to where the TV is sitting and as tall as the windows. That would create some mass that would offset the large fireplace. Don't abut them up to the fireplace, leave the same space as that between the window and fireplace. Use the space to mount sconces on either side of the fireplace. (You could use the lanterns that are on the hearth, Just hang them) Then get a larger mantle.

Teresa Smith I just noticed the extension on the bottom- I would definitely trim that so it's the same on both sides. Then you can match the built-in to the window.

collettec I would do a more substantial mantel that spans the entire width of the fireplace. I would also position it higher. Something like halfway between where it is positioned now and the middle molding of the adjoining window. I agree with others about a unit on the other side that matches the size of the window, with an area for the television there.

Creatively Yours Custom Inc. There is a certain type of wood look product that is certified safe to use to build a frame out around the firebox opening. Then you can add height and width and visually make the firebox look more substantial. Carry it to the end of the stone and then add a substantial mantle above it. Since i see wrought iron in the room's chandelier, you could add an oversize decorative metal medallion higher up on the stone wall. A little black also grounds the room and that fireplace wall.