This KB article shows how to give administration permissions to a user for a single folder.

You must be an administrator to perform these actions.

1. Click Workarea > Settings > Roles > Built-In > Folder Specific - Folder User Admin .
2. When you are in Folder User Admin, in the Show Drop-down choose CMS Users .
3. Click Add Role Member and choose the user.
4. Click Save .
   
5. In the content view, choose a folder and click View Permissions .
6. Uncheck Allow this object to inherit permissions .
7. Click Add Permissions .
8. Choose the user and then click Save . 
9. Set the permissions for this user, then click Save .