I'm not sure I understand your questions, but here's a guess.
Are you trying to import an object with multiple faces (like a building that has sides and a roof) and then apply a rule to it which distinguishes between the facades and roof? Yes, this can be done with a CGA rule. Check out the rule Esri.lib/rules/Buildings/Building_Mass_Texturizer.cga. In the Generate rule, a comp split on the faces is used to separate out the Facade faces (vertical faces) from the Roof faces (aslant and horizontal faces).
comp(f){ vertical : Facade
| aslant : RoofPlane
| horizontal : RoofPlane }
Are you wondering what files you can import into CityEngine? Here is a list:
Importing Data