Material is a type parameter for a wall. You can get its value with FamilyType.CompoundStructureLayers from Clockwork. If the material parameter of your door is an instance parameter, you will set it with a Element.SetParameterByName node. If it’s a type parameter, you could for example set it with SetParameterByName(TypeOrInstance) from Rhythm. For further details, you will find a lot of related threads through the search field, for instance:
You can also take a look here for general notions:
http://dynamoprimer.com/en/08_Dynamo-for-Revit/8-3_Editing.html
http://dictionary.dynamobim.com/#/
If you encounter some issues, please post a screenshot so that someone can give further advice…