Here is a simple question with a simple answer on materials and solids:
Question: Is there a way to retrieve the material of the solid geometry object of a Revit Element, like the door leaf of a door element?
Answer: No, I am not aware of any way that a material can be assigned to a solid. The only representation of the solid in the graphical user interface is through its faces, and they can have materials assigned to them. As far as I know, the solid itself has no such property. The only way that I am aware of to determine the material of a solid is through the path Solid > Faces > FaceArray > Item > Face > MaterialElement.
Another short little note on a completely unrelated topic:
In case you ever have problems with the installation of Revit, the Autodesk Revit Architecture Services & Support area includes a page describing a method to achieve a clean uninstall of Revit 2010 products.