Materials
By default, archipack set "dumb" materials to objects.
You may want to setup your own default material library in a startup file.
Archipack will then look at scene and use allready present materials by name.
In order to know the name of materials in use for each kind of objects, simply create one.
Archipack does provide a material loader taking advantage of libraries of predefined materials.
Doing so allow to re-use materials across projects, and quickly set all materials of objects.
You may also use a startup scene with common and default materials.
Download default cycles material library sample
In addon preferences, there is a "material library path", use this to setup a path to a folder with material libraries in .blend files.
Archipack will load material from those files using material names.
Archipack objects use more than one material so "Material Sets" are predefined groups of materials.
In N panel, you'll find "Archipack Material" with a dropdown list and +- button to choose/store/remove predefined material sets.
Materials sets are not materials, only a list of material names for each object's parts.
If not found in current in scene (by material name), archipack try to load materials from libraries when you create an object and when you choose a material set.
When you save a set, current material names are saved, so you have to ensure the materials are stored in your libraries.
Material sets store material names only, so you may use different sets of material libraries eg to handle more than one renderer.
Removing a set dosent remove material. This only remove the set definition.
Matlib vx addon may be a great help here, to manage your libraries.
Chocofur.com is currently working to provide a default cycles material library for archipack.