Of all the fireplace pics i have saved down, not one has a raised fireplaced w/o a raised hearth! However, I did google "wall mount fireplace photos" and tons came up. Most are more contemporary looking, so not sure what style you are looking for, but there were a couple with a stone wall.

I would use the marble you have in mind all around the fireplace and just float a ledge mantel above it, as someone suggested above if you must have one. However, I think it would look better without a mantel and just let the beauty of the marble be your decorative statement and element. I cannot tell how high your ceiling is from the photo, but would be inclined to run the marble up to the ceiling. If you don't like that look, You should go at least as far above the FP box as you will below to the floor with the marble. Unfortunately, it looks as though your builders put the electrical switch and outlet (on the right hand side) just in far enough towards the FP so that you can't extend the marble tile to the right as far as to the left (end of that wall). I'd ask the electrician to move those things before you start tiling.

Is it a prefabricated mantel or a custom fabricated assembled on site mantel? Pictures may help.

Thank you! I have to get the tile by Monday! I‘m also looking for opinions on tile size. The space is approximately 9’ long by 4’ high. The fireplace is 6’ x 2’. So the tiled space will be 17“ on each side of the fireplace and 12” above and 12” below. Could I use a 12x24 tile or do I need to go smaller? Thanks!