[nota]

I use 5v galvanized steel extra long [bought a change order cheap brand new]
so lapped the peak 6' and bent down the fascia edge 90 deg with every other steel sheet doubled
on top of 3 layers of 5/8 ply screwed and glued then lined up the steel edge screws on the beams
my spacing was 24'' centers on the beams so 24'' steel was used with extra long screws 2 1/2 vs 1 1/2 code and up sized also the thickness

I like the steel for being stronger then alloy and 5v for being able to unscrew a sheet to get at a leak in the future but staggered ply sheets should not leak anyway as I have an effective one piece roof with no plywood gaps

all plastic ''tar paper'' replacements ice and water peal&stick for metal roofing was used on top of the plywood with a nailed to code plastic under layer [fought that hard but had to use nails

no local roofer would bid my job my way
so I hired neighbors with some roofing exp to do it my way
the idea was cat 5 proof roof not local standard that is 120mph
I wanted 200mph proof roof and think the laps on the peak and the bent down out side edges
go a long way to stay put with out the danger of flapping and coming off in extra high winds
and for the cherry on top 5 SS 1/2'' cables rated 22k working load strap the whole roof to the concrete ground slab

over done YES but that is how to keep a roof in a cat 5

watched the home next door being built now
one layer of tar paper no tar or cap sheet then nailed on shingles over one layer of plywood
I guess a 100mph wind will destroy that roof
and they sold it for 394k for 1800 sf no garage nuts ?