I've been building conduit structures on the playa since 2004, love 'em. I've designed several over the years, for a range of uses, and all the structures are still enjoying their playa usefulness. Two people can easily get a structure over 1000 square feet framed up in under an hour, and if the wind's cooperating, it doesn't take much longer to get the roof tarps on.
I've worked with a variety of heights, material thicknesses, and other aspects and here's what I like best. For fittings, I go with galvanized steel when possible. A bit more expensive, but worth it to keep them from rusting. For conduit size, I prefer 1 inch EMT conduit. 3/4 inch works, but in really windy years the pipes were more prone to being bent, and I when the dust was really raging I couldn't keep myself from worrying about how the structure was holding up. On a 1 inch EMT structure, once it's up that's never a question - the playa can do its worst, and not only can the structure take it but you barely feel it inside. You can do the roof in pretty much whatever size you want, it's a modular and flexible concept. I've done a few with angled roofs to accommodate larger structures (domes) inside, but if you're going with a flat roof it's easiest to work with 10' conduit lengths. For vertical height, I've been using a 6'8" vertical height which has worked out really well (though you can go with whatever height you like). I'm tall enough to be able to put it up without a stepladder or milk crate, and it's tall enough that there's at least a foot clearance above most tents. That foot is essential, since the roof tarp will radiate heat downwards and you don't want it radiating into the tent if you can avoid it.
For the roof tarp, I use silver on silver tarps to radiate as much of the sun's energy away as possible. I use white tarps for the sides - they're less efficient, but they're brighter, and keep the place from feeling like a cave inside. Straight up vertical walls are easier to manage (since you just secure them to the conduit frame's poles), but put up more wind resistance. I go with 10x10 white tarps for each of the side sections, and then pull them out on an angle. In years past I'd then just stake them down at the bottom but in windier years there would invariably end up being some grommet holes that get torn up or the occasional issues with stakes coming up during a dust storm. This year I went with sections of conduit at the bottom of the side tarps. The conduit was staked down (using an 18 inch "hurricane stake" instead of rebar) and secure, and the side tarps connected via ball bungee. Easy to set up, and while I didn't get much of a chance to see how they fare under the most brutal conditions, I believe they'd hold up a lot better than staking the tarp directly into the ground. I usually put walls on three sides and leave the front open.
The fittings, bungees, and stakes all pack and store easily in a couple flip-top bins. There are a few different places online (and possibly someplace in your local area) where you can get the fittings, though I have a regular supplier out of LA that I buy from. Cool people, when I lived in LA I was able to do local pickup but they have reasonable rates for shipping via UPS so I've just kept going back when I need more hardware. PM me if you want their info.