For GKE version 1.7 and later, the Pod address range can be from any RFC 1918 block: 10.0.0.0/8, 172.16.0.0/12 or 192.168.0.0/16. For earlier versions, the Pod address range must be from 10.0.0.0/8.
You can customize Pod address range by specifying a CIDR range. For example, you could specify the range 10.96.0.0/16
gcloud container clusters create [CLUSTER_NAME] --no-enable-ip-alias \
--cluster-ipv4-cidr 10.96.0.0/16
where [CLUSTER_NAME] is a name that you choose for your cluster.