Little Black Egg
Finding components to build this in Burma might get tricky, but this is the most tested, safest home grown gas (propane) oven. It should be convertable to natural gas and will have no problems with up to 100 pies a day, although if you encounter especially busy times, you might want to build two.
You have access to multi-ton presses? How cool is that? I'm envious. Really envious
I guess you are sort of on the side of the planet where stuff gets made, huh?
When I was in college, minoring in ceramics, I built a kiln. It was made out of regular clay bricks, arranged in a box. It had two openings- one in the bottom corner and the other in the top corner on the opposite side. I pointed a directional gas burner in the small hole, a smaller version of this burner:http://www.sz-wholesaler.com/p/1068/1110-1/gas-burner-dlr34t-554361.html
It was a salt kiln. The kiln was brought to temp over about a day, then the salt was tossed in the bottom hole, the burner was turned off and the kiln allowed to cool. The pieces turned out quite nicely.
I bring this up because, if I was building a gas fired oven for pizza, that's probably how I'd approach it- a single, powerful gas flame directed into an insulated weatherproofed, firebrick box. It would most likely take a tremendous amount of tweaking to work well, but it would be a design that I would feel comfortable/safe with. Anything more complicated than a single flame burner is outside of my realm of expertise.
Don't get me wrong, I fully understand the thermodynamics of gas deck ovens and, if you find plans, I'll give you my opinion, but choosing a burner, placing it and making sure proper combustion is maintained, I wouldn't feel comfortable with that.
I guess this is my really long way of recommending an LBE
If you can find a Weber(ish) (round) charcoal grill, that's the way to go for less than 100 pies a day. Once you're doing more than 100 pies, then you should have plenty of money for a real gas deck. This one from China looks pretty good:http://www.pizzamaking.com/forum/index.php/topic,18793.msg192392.html#msg192392
Marble, by the way- very bad for baking. It has very little resistance to thermal shock and most likely will fail- and possibly dangerously. The idea of a second stone on top of the steel is a good one, but you need to with something like firebrick or cordierite.