Just waiting for the pearl clutching crowd to tell you how you are going to blow yourself up....
Sounds like you have a decent grasp on the fundamentals, but I feel we need more information. I have worked with gas on multiple occasions and it is relatively straight forward. Depending on size of fireplace and length of pipe a 1/2 line would probably be sufficient.
I guess I dont even know what you are looking for. Is this going to be a primary heat source or something you use for an hour or so a few times a week? Heating something as small as a bedroom with a 25-50k BTU gas fireplace is gonna make it HOT in there in a hurry. A normal sized furnace is about 100k btu and it heats an entire house.
Personally I like vented fireplaces more, but vent-frees are so dang easy to install. So if it is going to get regular use I would say find a way to get a more complicated vented fireplace, if its going to be a limited use thing a vent free might work.
I still dont know why you want to build a fireplace, could you send us a picture of what you think you want? I feel like building something would be 10x more difficult and complicated then buying one ever would be. IME the price of the fireplace is minor compared to the price of running the gas and exhaust lines.
OK so here are my questions:
1. Picture of what you think you want.
2. How much use?
3. How big of room?
4. What time of climate do you live in?
5. How far is this from the gas meter?
6. What your experience level/How much are you hiring out?
To be honest, I just have an unused corner in my bedroom that I thought a fireplace would look nice in. Not for anything other than ambience - not a primary heating source. I originally was going to go the full-masonry route, but i have since learned that adds a ton of weight to your house, and you need to re-inforce the flooring when adding so much brickwork, so I thought a gas fireplace with stone veneer would look just as good.
Running the gas line really shouldn't be that difficult, the meter is on the floor below my bedroom and across a semi-finished utility room, so running the gas should be a breeze. Venting shouldn't be a challenge either - I can just go straight up to my ceiling, into my attic and out the roof (doesn't seem that difficult...?).
I would do it all myself, and really I am just looking for a fun project to do, and I figured running a gas line, a vent, and installing a burner and tossing some logs and fake coals in a box REALLY shouldn't be this hard, yet stores are charging easily over $1,000 for a metal burner and some gas logs. Heck, even if i went the fire glass route it wouldn't even cost that much!
One thing I guess I haven't considered is the "clean burning" air/gas mixture. I would assume that if I vented the unit it would burn clean from the natural gas, but if that is incorrect and I need to do more calculations, then i am probably toast.