As others mentioned... U value has nothing to do with the coverage . Whether you put tiles, slate, zinc or metal will make virtually no difference in the u value.
In terms of zinc - most refer to zinc and really mean standing seam. Zinc is the material. Standing seam is the shape of the roof panels. You can have zinc roofs in other shapes (tiles...) And you can have standing seam in other materials
Some previous posted a few alternatives. They are mostly coated metal . Other option would me aluminium.
Then comes the question about installation method...
Traditional standing seam(zinc) is rolled/formed on site from coils. Needs a specialist installer since not everyone owns the forming machine and knows how to work with the material.
Most of the coated steel and aluminium comes in form of pre formed panels .
Then there is only the seam to be closed on site with a seaming machine .
And last not least there are click systems , where you can install without the need of machines/seamers . Panels come preformed .
So it's really
1. Which shape you want (standing seam I presume from your text)
2. Which material do you want ( zinc=most expensive ; Alu= mid price; steel =cheapest)
3.which installation method you prefer (fully trained specialist = most expensive, general builder/roofer= mid price , self install DIY =cheapest) in point 3 : makes not that much sense to buy a DIY system and then hire a trained expert to install it.
You might as well go with zinc in that
Scenario