The decision to build an on-site concrete mixing plant probably has more to do with how close the closest mixing plant is to the factory than the amount of concrete used.Giga4 is building an on-site cement making plant. Is there a particular reason why Giga4 is using so much cement while GF3 was mostly steel? Something to do with the properties of the land? Cost of materials in the region?
Giga-Berlin will probably use similar overall construction techniques - with similar amounts of concrete and steel.