it's not aluminum nor zinc

it's ZINCALUME - zinc and aluminum alloy

and either material is common roofing material. it's been used for ages, besides the ubiquitos concrete / clay tiles

i know cos i design roofs - engineering side, not architecture

for no.2, read my earlier post. clay tiles needs waterproof layer (in this case, metal sheet is the cheapest and easiest and last longest)

AND REGARDING PITCH ; it doesn't matter what degree your pitch is. it depends on the type of roofing material and profile

if you use seamless metal sheet with klip lok profie, you can go as low as 4(deg)
if you use tiled rooginf, it's recommended to be at 25(deg)
as long as you don't go below 5(deg), you should be ok. lower than that, then consider reinforced concrete flat roof (major headache)

the only reason why pitch is extra important is in 4-season country where high roof pitch is needed so snow won't settle on the roof. snow = extra weight and will make your roof collapse

learn more. roof pitch has nothing to do with sunlight. it's either snow or roof design or just for styling,

for no 3, you still need the chicken wire netting. if not, how will you put the rock wool? u surely needs something to support the rock wool and that's why the chickn netting is there