I would think that the center layer is the ground in this circuit.
If we want to create the regular layout, draw the layout as RealAEL has described. But obviously, there are no circuit/schematic models to simulate this type of layout, and we need to use EM analysis.
For efficient EM analysis with Momentum, the "simulation layout" would be created differently than the "regular" layout: In Momentum, you can map the ground as a "slot" layer instead of a "strip" layer. This with mesh the slot instead of the metals, and use a "magnetic current" approach for more efficient simulation. To use this slot layer simulation, you need to draw the layout where there is NO metal. In your case, you draw the hole instead of the metal.
Top and bottom layer: map as strip layer, draw condutors
Middle ground layer: map as slot layer, draw hole