For Google to build their own fibre optic networks, that will be able to accommodate a lot of the USA and Europe, what's the costs/difficulties? I am aware the

For Google to build their own fibre optic networks, that will be able to accommodate a lot of the USA and Europe, what's the costs/difficulties? I am aware they were trialling some sort of netwrok locally to CA, how difficult/expensive is it to roll this out worldwide?