Firepit, anyone ever built a propane one?

I have this steel water tank on our property that is just collecting water and becoming an eye sore, I was thinking today of building a gas firpit out of it, I found lots of things on google on how to build them but mine is 6' in diameter not three like most of these... Im interested in using the whole 6 feet
here is a search I did on google
[ame="http://www.google.com/search?hl=en&safe=off&gbv=2&biw=1360&bih=610&tbm=i sch&sa=1&q=glass+firepit+propane&oq=glass+firepit+ propane&aq=f&aqi=&aql=1&gs_sm=e&gs_upl=11379l12014 l0l12205l5l4l0l0l0l1l181l259l1.1l2l0"]glass firepit propane - Google Search[/ame]
and here is a what a slightly smaller version looks like
http://www.skyvalleylandscape.com/im...irepit_day.jpg
anyhow Im curious to know if anyone has done one of these my main concern is how deep to lay the lines under the surface as I do want a decent height flame and I also wanna use the full 6 feet doesnt have to be SOLID across 6 feet but I defintely want it to go to the outter edges of the pit for marshmallow roasting access! :D
Any other pictures are helpful as well
Thanks!

here is where mine is going, it will be filled with decomposed granite for a base and HOPEFULLY also a topper since it is so cheap out here
http://a4.sphotos.ak.fbcdn.net/hphot..._2560699_n.jpg

How are you going to run the line(s)? One single line that runs the whole diamater, or something snaking? Also, are you going to run it off of a 20 lbs tank (standard gas grill tank), or something bigger?

*IF* it were me, I'd find an old gas grill to donate some parts. Then use steel pipe with holes drilled in it to make a burner. The question is one single long burner, an "X" shape, or a snaking twisting burner? In any event, I'd feed the burner from more than one location to ensure an even flame along the burner.

Maybe something to consider would be to look at propane forges. Those guys are fabbing some great things and it may give you some ideas for burner construction.