Building Themes supports district styles. You can easily create your own district style in content manager and publish it with a single click. That is the most straightforward method.

One restriction: District styles can only contain workshop items, not vanilla buildings.


There are a bunch of theme mods on the workshop (see this mod description). Basically the mod is only made of a single .cs file in the Source folder that defines the name and description of the mod, and a BuildingThemes.xml file.

The xml file contains all the data required for the theme. To create such a file, I would suggest you to look at the source of other theme mods.

You can take an existing theme you created ingame from the file {Steam folder}\steamapps\common\Cities_Skylines\BuildingThemes.xml (this file contains all of the themes you created).

The file structure of a theme mod looks like this:

• MyMod/
  
  • BuildingThemes.xml -> contains theme data, parts copied from the other BuildingThemes.xml in steamapps.
    
  • Source/
    
    • MyMod.cs -> contains title and description of the mod to display in content manager
      

After creating those files and running the game, it will create a dll file for your (MyMod.dll). That's the compiled mod.