One way of doing it is like this:
First the end result:
The family is build up like this:
Notice the void forms
Notice that the length and width parameters are instance parameters. The void sweeps and the solid sweeps are created by a profile.
Next I have, in the pyramid family, mapped the parameters from both profile families mapped to the same instance parameters in the pyramid family.
Be aware that the parameters in the profile family have to be type parameters. So if I change the angle both profiles change accordingly.
A nice feature from Revit 2014 is that you can now schedule Generic Models.
If you want the revit files send me a message through LinkedIn.