...
You'll need to provide Google with the URL for your SAML-based SSO service, as well as the URL your users will be redirected to when they log out of a hosted Google application.
Use the following URLs when you are configuring for Google Apps
Sign-in page URL: https://yourCasServer/login
Sign-out page URL: httphttps://whateverServerYouWouldLikeyourCasServer/logout
Change password URL: http://whateverServerYouWouldLike
...