Multi-Layer Cities

[TheHedgeTitan]

Does anyone know if there is a mod or method that allows you to build layers to your city - platforms that can be built on and under?

[grapplehoeker]

Unfortunately, no.
There is no real z plane. The best that you can achieve with the Move It mod and others, for example, is to terrace the terrain and build over or under, but adjacently.
If and when there is a CS 2, perhaps, and with any luck, they will implement voxel terrain dynamics. This will enable terrain to be modified in ways that would allow structures to be built over, under and even on the sides of terrain.