I would stay in the 24-26 gauge range to prevent oil canning, and make sure you hire a good trim bender or make sure your roofer knows one. The roof in itself is simple but the trim metal is what really seals everything up and makes it look good.I’m definitely thinking standing seam metal. I am fine with the look (very common in the mountains for the snow shedding!) and verified my HOA has no such stupid shingle-look restrictions.