It depends on what ninjas do you already have now .. If you have ninjas that can support Roshi, then maybe you can consider getting him now .. But if you have nothing, then go for Ay 3rd for now, going for Land of Lightning Treasure ensures you to have a complete team (Getting Samui and Omoi while going for Ay 3rd) ..

If you're watermain and have sakura sailor then you're good to go for Roshi .. Then maybe draw10 in GNW treasure to get Fukugi or if you have Han, use him with the team .. Lightning Tiger summon and you'll be fine ..

np .. just use all your good equipments and magatama/runes with roshi and also mood him max ..