A good shot of the completed firepit last August.
I waited until the following April to post this project. I wanted to see how it held up all winter before encouraging anyone else to do this. My son and I tried to level a few spots out with mortar, but only made a mess and went back and chiseled it out. GET YOUR FLAGSTONES LEVEL the first time, you'll be glad you did. I've had to repair a small gap or two where the bermuda grass has crept in. Some charcoal starting fluid and a lighter have gotten rid of it in a few places and it hasn't came back. This project is 'easy' in terms of details, but it was a lot of down on your hands and knees work. BTW, the stones are level with the lawn, and you're looking at all the maintenance done 100% with a riding mower. I can put the left front mower tire on the flagstone and make a quick lap in under 10 seconds, so the maintenance is super-easy as well.
Next I plan on coating it with a clear gloss concrete sealer, first because I prefer the wet look, and second I'll bet less water under the stones will make it last longer, and perhaps keep the grass from coming back. Feel free to chime in with suggestions etc, and I'll edit the post if it will improve someone else's work efforts.