Aside: I know what they look like wet...I used a deep penetrating sealer on mine to bring out the warm tones in the house

You can use them indoor or out in most climates...the slate has a mesh backing so there's design consistency in the pattern. I just love em and am still very tempted to overlay my concrete pool deck with them, freeze cycle be darned
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Bassaddict, sorry about the side comments and my excitement to see "my" slate on Matt's deck, BUT I may have a few thoughts for you as a result
I looked into retrofitting my pool deck with a permanent fire pit, but didn't end up doing it because I ended up needing the freedom to move it for winter to install the dome that allows me to swim in winter up here. So presently, I'm using a portable propane one, which has worked out well as I move it to my house deck in winter for pre-swim warm up
If you're installing a gas line anyway for a heater, then the cost of the extra bit of run is likely reduced a great deal and permanent is normally the way to go.
If you want to save a bit of money, a buddy of mine built his own and said it was pretty easy. Wish I had a pic for you or knew where he sourced the gorgeous black polished stone topper he put around it.
But in a new build if you're not sure how you're going to use the deck, etc., you might also just want to get the gasline close to the area and cap it, then decide after a season where you actually want it/will use it most, and experiment with a portable one in the mean time.
It kinda depends on how generous your footprint is.
They're about $400 at a big box store, so a low-cost experiment compared to a permanent installation...at least compared to the components I was looking at, which were a few grand before installation.
Is you deck all flagstone, or were you referring to constructing it out of flagstone?
Or did you want to offset a pit area like in the pic below?
Also, have you considered a Fire Table? I've found that people enjoy being able to set their drinks down, and that you then have the daytime utility of using the table. Something like this might be the best of both worlds:
Sierra Linear Fire Pit Table | WoodlandDirect.com: Outdoor Fireplaces: Fire Pits - Gas, The Outdoor Greatroom
