Watching a TV build show they used light weight steel rather than pressure treated etc. for all the joists and beams

What type of gal steel ga etc

pros or cons in this type of build

I see trex sells it but any other source?

pic

Perfectly straight and level vs cost? Perhaps issues with approval.

I would guess that the joists are 20 ga. steel. Most structural members run 20-14 ga. Looks like 8" or 10". Joists have a C-lip for added stiffness. Beams are probably same guage and either a track or U channel.

Mostly see steel framing in a commercial setting and generally in a non-bearing application. I would guess primary use is for partition wall framing. I haven't seen it used much in exterior applications, but should hold up ok.

Advantages include ability to get long members, consistent quality, and as jonr mentioned, none of the issues associated with lumber. Properly designed there would be very little waste and approval should not be a problem.

Lots of suppliers available, mostly catering to the commercial side.

I'm doing kind of a hybrid system with the screened-in deck I'm building: PT lumber for the main structure with steel ledger and joist.  Call me anal (everyone else does); but since I'll be using composite decking and will be able to see it through that 6' wide glass patio door, I wanted everything to be as straight as possible... and stay that way over time.  I did a lot of Yahoo searching on the topic and found some great articles.  I don't still have the links to share with you; but they're out there and IMO easy to hunt down.  I tried to source some generic galv stuff since the Trex system is rather pricey; but I couldn't find anything local and the price to bring in the small amount I needed killed any savings over the Trex.  I will say it's a nice system: multiple anti-corrosion layers with a matte gray/black powder coated final layer.  They only come in 1 gauge; which was thicker than I needed for my 10' span.  The recommended screws are crazy expensive.  I found it a very easy system to work with... I also have a strong metal-working/fabrication background.  Even without that, though, anyone decent with tools should be able to do very well with it.  I do intend to hook the deck up to a couple of grounding rods.  If the price doesn't scare you off, I'd say it's a great option.