I have a Fireplace Xtrordinair natural gas insert (made to go in an existing fireplace), but FPX also makes fireplace units for new construction.

No problems w/ the FPX in the two years I've used it. I've posted several times about this unit on this forum in case you want to do a search.

FPX offers fireplace units in various sizes & BTU outputs. You buy the firebox size you want & choose a faceplate (several styles & finishes available). I haven't bought a fireplace, so have no knowledge of how you "finish" one, but I believe FPX has an alliance with a company that makes mantles, etc. if that's the look you want.

My info is two years old, but FPX did offer an optional remote control to turn the unit on & off, operate the blower speed (if it has one) & control the flame height. Other options included a thermostat to turn the unit on automatically (like a furnace) & a ducting system to share the heated air with an adjacent room. The FPX can operate as a radiant heater in the event of a power outage, but would need a backup power source if you wanted to run the blower.

In terms of maintenance, FPX recommends an annual cleaning & inspection. I confess I waited until this year to have that done, and the service guy only needed to vacuum out dust & clean the inside of the glass -- said the burner, etc. looked fine.

Other manufacturers probably have similar features. The various manufacturers offer different interior & exterior appearances, so, if possible, visit dealers in your area to see the ("live") units in person so you get a feel for what you like.

Check the BTU ranges & efficiency ratings. Your choice may depend on if you want the unit to be a heat source or more for ambiance. Some units come with a blower; on others, it's optional. Most units will work with LP or natural gas, but ratings might vary w/ the fuel source.

If you want to operate the unit in the event of a power outage, make sure it's capable of doing that.

One trend in fireplace units is to have a huge, "to the floor" viewing area w/ the controls "hidden" on a wall elsewhere rather than built into the unit. "Town & Country" is one brand that does this. I know nothing about the company or how convenient it is to install/operate the unit, but I saw one on display at our local stove store & the appearance was impressive.

In addition to FPX -- which is part of Travis Industries, along with the Avalon & Lopi brands -- the Mendota and Harman brands get good reviews on this board.

Another option might be a freestanding gas stove rather than a fireplace, but, again, what "look" you want -- as well as your budget -- may determine your choice.

The only other point I can think of right now is, work with a good, reputable local dealer.

There are lots of options out there. Most of the manufacturers have websites, with varying degrees of usefulness. I found that with FPX, for example, the brochure I picked up from the dealer was much more informative than the website (again, that was two years ago). The FPX site does have a great "design (photo) gallery" in case you want to get an idea of how their unit styles fit into varius room designs (traditional, period, contemporary, informal, etc.).

Good luck w/ your research.