I've designed one, but we've yet to build it. I did a quick search and found some videos that might help.

Here is a link that might be useful: Youtube Videos on building a surround

I replaced the surround at the time that my kitchen was being remodeled. As the home is open concept, I wanted the surround to match my kitchen cabinets. It was designed with the assistance of the KD who ordered the appropriate molding and trims from the cabinet company. She also drew a front and side view for the carpenter to follow. I was pleased with the result. Since your situation is different, I would think you could show your carpenter pictures or a sketch of what you want and he could order the appropriate materials. If you are building it yourself, an online company that sells corbels and special trims could be of assistance. There's also home depot or cabinet shops.