I have a large feature wall in our family room with 3 alcoves across it. the center piece has an alcove over the fireplace mantel. I would like to build bookcase on either side, fill in the gap in the center and put moulding on the entire wall. This wall is fairly deep to house the fireplace but i feel it takes up more space than needed. not only would i like to reclaim some of this space for this narrow room but i would like the bookcases backset enough to get a 3 dimensional look to the wall. The contractor is basically planning to cut back the bookshelf spaces by a couple of inches to get the dimensional look. i dont think this will be enough. Is there a general rule of thumb for this?