If you are considering a ventless gas fireplace you should read the many discussions about their safety on the GardenWeb Fireplace Forum and elsewhere. Because their safe use depends on proper installation (even the log arrangement) and the ability of a detector in the unit to turn it off when the CO level is dangerous, I will not specify them. Here is a quote from Consumer Reports provided by Grinder12000 on the Fireplace Forum: "An unvented gas fireplace that's safely sized needn't pose any acute health hazard. But our tests confirm that these heaters contribute significantly to indoor air pollution. If you're planning to buy a gas fireplace, a vented model should be your first choice. That's especially wise if any household member has asthma or another respiratory ailment that may be exacerbated by particulate matter, or if your home is very airtight--and so will disperse the fireplace's emissions less readily." "A vented gas fireplace needn't cost more to buy and install than an unvented model, since some units require only a fairly small vent pipe that runs horizontally to any outside wall." "If you do decide to buy an unvented gas fireplace, here's how to ensure it operates as safely as possible:" * "Observe GRI guidelines. Insist that the contractor not exceed them when sizing your fireplace." * "Limit its use. Though occasional extended use of an unvented fireplace should pose little long-term health risk, we suggest limiting operation to no more than a few hours at a stretch, as a rule." * "Provide extra ventilation. Leave at least one window open in the space where the fireplace operates." * "Buy only a certified package. Some fireplaces are sold as two separate components: a "firebox" and a "logset"--the component that contains the burners and logs. Ask the contractor to confirm, through the owners' manual or an American Gas Association label on the logset, that the two components are compatible. A dealer sold us a fireplace firebox with another brand's logset he claimed was suitable. He was wrong; the combination emitted higher levels of carbon monoxide than is desirable until we obtained a logset that was approved for that firebox." * "Use a CO alarm. That dealer error aside, the fireplaces we tested showed no propensity to generate any carbon monoxide (CO). Also, some models claim to shut off should carbon monoxide levels ever rise. However, we recommend use of a CO alarm with any combustion appliance, including an unvented fireplace." Here is a link that might be useful: Fireplace Forum

I know you said that you aren't changing the carpet, but might you consider it? Only because, I'm assuming that is a gas fireplace, there is no need for a large tile area in front. You can go for a narrow hearth or no hearth. If you wanted to do that, unless you have a large scrap or can match it, you're stuck with the large hearth. I like the idea of doing built-ins. As they would be asymmetrical anyway due to window placement, you may just want to build in on the right to accommodate TV and components and leave the left side as is. Not that I'm suggesting this style, but just to illustrate a tv next to fireplace built in, one side only. Something like this might work for you, but without the overmantel. Note that this tile surround is very similar to your hearth tile. If you like that look, you could get more tile, perhaps and then tie it together that way. [Eclectic Living Room[(https://www.houzz.com/photos/eclectic-living-room-ideas-phbr1-bp~t_718~s_2104) by Shallotte Fireplaces COASTROAD Hearth & Patio

Here we go. I used your tile, well, because it was easier to do so since it was already angled correctly. The program I use has no way to reshaping things. While drawing it, I decided I'd like the wall above the fireplace angled too, so I did what I could to make it look that way. The program I use MS Paint, so there's only so much one can do. I've yet to get Power Point added to see if I like that better. In real life you could use smaller tiles on the side (here it would be leaving off the narrow tiles if it works with code for the fireplace, I don't know about gas, we have wood burning) to allow for a wider wood surround.

Able to post one at a time. Here's wider view of area.