First of all, what IS your starter? If it's Turtwig or Piplup you should train in that tunnel connecting to Oreburgh.If it's chimchar... well, just train on the route above Jubilife City.
When to stop training:
When Turtwig is at lv.16
When Piplup has eveolved into Prinplup
When Chimchar has evolved into Monferno and learned mach punch
When budew is about the same level as your starter
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Hope I helped! Good luck wtih Roark!