You can use 3/8 oz. Cu on RO Dk for outer layers, 0.5 oz for Epoxy clad layers and 1 oz layers for Vcc and ground for strength on uneven etched signal layers to prevent warp.
Also 1oz gives lower conduction losses, and lower crosstalk with appropriate prepreg in between also. As well better tolerance on 3/8 Oz fine line copper over RO Dk. (ROgers Dielectric constant) but blind or buried vias adds cost to process to fabricate and verify reliability.
There are many types of epoxy/glass ratio FR4 and different weave patterns and. fill factors, whichaffects Dk andloss tangents greatly, vs GHz .