how to model a ground plane on CST MWS

I am new to CST MWS. I want to model a ground plane as part of my simulation.
Is it correct that I model a brick with material copper as a ground plane ? also I don't know what should be the height of plane? I know the width and length, but I don't know what should I enter for Z?
Can any one help me with this?

What do you want to simulate? Depending on your application, a brick of copper can be right or wrong .