Multisite folder structure in Drupal 8+

Following is an example of the multisite structure with Drupal. For simplicity, other Drupal core folders and files are not listed.

Multisite structure:

-- core

-- modules
   -- contrib
   -- custom

-- themes
   -- contrib
   -- custom

-- sites
   -- site1
         -- modules
            -- custom
            -- contrib
         -- themes
            -- custom
            -- contrib
         -- files
   -- site2
         -- modules
            -- custom
            -- contrib
         -- themes
            -- custom
            -- contrib
        -- files
   -- site3
         -- modules
            -- custom
            -- contrib
         -- themes
            -- custom
            -- contrib
        -- files

Given a scenario where the entire multisite is maintained by a single person, only the files directories will normally exist in the directory structure below "sites". The modules and themes directories are only created in the webroot.

For more complex multisite environments, were multiple maintainers maintain their own site code, this may not apply. This complex scenario is expanded in the next section.