Here's CE help
Help -
The relevant section is CGA Shape Grammar Reference --> Shape Operations
basically, assuming you have an attribute in your shapefile for Z_Value you'll need to define it in the rule file then you can use it with the translate function:
attr Z_Value = 0
Lot-->
t(0, 0, Z_Value)
(I think it depends on how you have your workspace set up as to whether CE uses y or z as up.... I can never remember)