how about a mason?

So much depends on the overall look you want for your home. That determines the size and placement of the fps. Exposed beams and stone of any sort sounds traditional. For your great room, I'd go for a raised hearth and a surround, mantel and overmantel that are in scale with the room. And that means large! The trend here in master suite fireplaces is to mount them about three feet high without the traditional wood fp trappings at all. A matter of taste. I put in three-four fireplaces in every home I build; and none in any home are the same. For instance, below is another fp in the same home as in the "building a home thread" thread. But since this is the kids' play area in a small basement room (as you'd probably guess from the photo), we scaled the fp accordingly. Kingsman gas fireplace, Century Stone concrete brick surround, raised Indiana limestone hearth

Whatever you use around the sides and top of the fireplace, you can use on the riser. I took out the raised hearth for my fireplace and used a tile surround. I also tiled the area in front of the fireplace with the same tile as the surround. I believe that you need at least 16" of non-combustible material in front of the firebox. Here is a link that might be useful: some examples of fireplaces with risers

We have both. We did a raised hearth in our living room. A wood burning fireplace, not gas. Did the raised for a few reasons. Although the fireplace opening is fairly large, I wanted it raised for sight lines. I wanted it raised for the same reason Weedy wrote, that it actually does provide additional seating when needed. The raised hearth also makes access easier for me when tending the wood fire. My kids were young, 3 and 5 years old, when we built this house. Though the hearth could be considered to be a hazard of some sort, it also acts as a "stopper" or sorts, keeping the kids from running around right in front of the fireplace opening. My kids loved the raised hearth; sitting and watching the fires, warming themselves, etc. In wintertime it was one of their favorite spots for sitting and reading. There are differences between gas and wood fires, so your priorities may vary. Upstairs in our master bedroom suite I have the firebox raised off the floor, maybe 12" or so...but instead of raising the hearth too, I built the hearth itself flush with the floor. Up there I didn't want a raised hearth at shin level when someone was moving around in the darkness. We wouldn't ever use a raised hearth up there for sitting, we have a couple of reading chairs set around the fireplace. Though the room is generously sized, I didn't want the raised hearth projecting into the room. Raising the fireplace box itself still gives nice sight lines of the fire from throughout the bedroom area, even when in the shower or tub in the master bath, and the "flush with the floor hearth" preserves some square footage. So for us it was two different rooms, two different sets of priorities. And do realize your kids will be young and reckless for how long? Whereas the hearth will be raised or flush forever.