Instructions
Download a third-party mapping add-on for Call of Duty: Zombies, such as COD Radiant (see Resources).
Double-click the CoDTools.exe icon, and follow the installation instructions.
Enter the folder labeled callofduty/main/maps, and create a new, untitled folder.
Run the Radiant application and, when prompted, find the cod.qe4 file located in the toolsbin sub-folder in your "Call of Duty: Zombies" folder.
Click on the "Preferences" menu at the top, and select "Edit Preferences."
Customize your preferences according to your desired map. Options include face selection, light or heavy drawing, camera speed, texturing degree, texture brush options and others.
Use the toolbar at right to edit the 2-D map editor grid. Add terrain features, buildings, doors and other elements as desired.
Experiment with different lighting methods to create the desired lighting scheme for your map. Right-click on the map, select the "Lighting" option and choose from the many sources of light. You can also edit intensity and radius of each lighting source.