"Custom Reports option in the NetFlow Templates page is deprecated from Cisco Prime Infrastructure Release 3.2, due to high disk space usage. You can generate the report from the Reports > Reports Launchpad > Raw NetFlow page"
Actually I saw that 3.4 user guide earlier. But there it is saying 3.2 version. However, here under template it is showing as deprecated in the 3.1.7 version also. I have attached the screenshot for your reference.