Hi,
Here is an example of a pattern generate by VB script. This one is a bit complex as it relies on subroutines to generate the patterns, but you can reuse parts of it to suit your needs.
The idea is simply to create 3D blocks of small size (more or less the size of your FDTD grid) at regular intervals along the dimensions you need. This will create a “staircased” approximation of your design and will be usable in FDTD.
Aurelien