This is one eg of a sheet membrane system:
https://ardexaustralia.com/product/ardex-wpm-1000/
This is an eg of a liquid applied membrane system:
https://ardexaustralia.com/product/ardex-wpm-908/
The entire Ardex roof and deck waterproofing range can be found here:
https://ardexaustralia.com/products_category/waterproofing-roofing-membranes/
Ardex are a premium company, good products but they make you pay !
I've used the liquid applied membrane once, about 20 years ago but I've never used the sheet style membranes. I found the liquid applied product was difficult to apply neatly in the heat in Darwin Australia.
The sheet style membranes seem to have become the "go to" product for commercial projects from what I can gather.
The skillset and experience of the applicators should be your guide in my opinion...
PS I'm surprised that you're only getting 50mm outlets to drain the roofs, I can see theres multiple of them but personally I'd be looking at more like 100mm, will take more volume and be more resistant to blocking with leaves etc.