I haven't built one, but would like to. Search the web - there are lots of helpful sites.
http://www.diynet.com/diy/shows_dhsc/episode/0,2046,DIY_18179_34381,00.html

http://www.canadianhomeworkshop.com/quickfix/fire_pit.shtml

http://www.swingplans.com/fire_pit_plan.html

I think it would be fun to build one of these. Good luck.
Diane

my husband is putting a wildlife habitat in our back yard, called "A Wing & A Prayer" I have tried to talk him into installing a firepit too... but so far no bites, let us know us know how yours come out!! photos are always good!

I built one a month ago. I had a gas line stubbed up through the concrete decking of my pool when they poured it.

1.I got a 90 degree shut off valv and connected it to a flexible gas line (pick one up in the appliance section at local Home builder store).

2.Bought a fire ring from an outdoor furniture\BBQ store and connected the fir ring to the flexible gas line.(but you can buy the kit here. http://www.firelogs.com/HearthProductsFireRing.htm) scroll down the page.

3. I bought stackable blocks (like you would use to build a small garden retaining wall) and configured them into a circle (abot 15 blocks per layer, 3 layers high). no need to morter, just stack 'em.

4. Bought 10 bags of lava rock in the BBQ section of home builder store and poured them in under and then over the fire ring.

Now I just turn on the gas valve and light it. Works great. If you want pictures, let me know by email.
rgs@thesissons.com