First, select your fireplace, discuss your plans with Enchanted Fireside for best recommended installation options, and refer to the installation instructions specific to that fireplace (these can be downloaded from the manufacturer’s web site) before building the “bump-out”. The inside depth and width should be sufficient to enclose the firebox, insulation and sheetrock and provide required clearances to the interior walls of the bump-out. If the fireplace can be rear-vented, the lowest part of the roof on the bump-out should be at least 2’ higher than the height of the firebox plus the height of the platform on which the firebox will be installed (if any). If the firebox is a top-vent model, the lowest part of the roof on the bump-out should be at least 4’ (preferably 6’, especially if for propane) higher than that height.