29 gauge is the standard around here. It a higher tensile strength than the 28 they used to sell. It holds 15% more weight than 28ga before it deflects. I've been putting this stuff on for over 40 years, just did one again yesterday. If you think 29 is flimsy, try putting on 34 gauge as I did in the Dominican Republic last year, with purlins spaced 4' apart. But I would be cautious putting steel on in your environment, look around and see how other steel roofs are holding up.
One other thing about steel, snow will slide off, even on a 4/12 pitch.
