'Create a site with a different address' feature has been removed by Google Page Creator. This feature was introduced by Google on 21st September. With this feature one could create changed subdomain on Google Pages. The feature does not exists there anymore. You can view screen shots. It is little surprising as their help page still talks about subdomain feature. Some people feel that Google has dropped this feature owing to many spam pages being created by web spammers or their experiment might have failed and must be trying something new.