In my opinion, the best way to build a fireplace mantel is to use a story pole, take good measurements and snap a few pictures. A story pole is a length of narrow board, often a 1×2.

Pearl Mantels Shenandoah Pine Fireplace Mantel Shelf. At 60 inches, this pine mantel shelf has hand-hewn edges and can be hung with or without corbels depending on your preference.

Floating Fireplace Mantel. I f you don’t like a lot of visual clutter, you’ll love the look of a floating mantel shelf like the one seen here on this modern fireplace from @mccauleyinteriors ...

PROTECTIVE WALL FIREPLACE: This floating fireplace mantel shelf 60 inches is not only a lovely display space, but it also serves as a barrier between your valuables and the flames beneath them.