Since you have a High Availability solution available in Hyper-V with Failover Clustering, why should you consider Guest Clusters ?
Some reasons for considering a guest cluster, is when you need a High Available solution for your SQL servers.
Example: When SQL server is installed in a two-node Failover Cluster, the SQL Server service is installed on both nodes of the cluster. When one of the nodes fails, the remaining node will quickly take over the processing that was being done on the dead node.
If you only had a single SQL server VM in a Hyper-V Failover Cluster, the SQL Server would restart on the remaining node in the cluster, having time consuming tasks to be completed before beeing able for client requests.
Requirements for Guest Cluster:
You can only use ISCSI for guest clusters.
To build a guest cluster, you should follow the same steps as you would do for a 'normal' cluster, using ISCSI.