There would be insulation between the chimney and metal in these examples. If you're working with a general contractor, that's your first step in asking for a resource to put this in for you. Otherwise, search for fireplace specialists in your area. You didn't say, but if this is a do-it-yourself build, it's quite possible that you could work with a bricklayer and source your own metal from a metal fabrication shop to complete the design. There are also plenty of metal fireplace inserts that you can build around if you find one you like.