I just answered a very similar question here:
However, I also strongly agree with Jerry’s (@Gerald_Nickel) and @Dee’s comments. We don’t have enough information to tell you what to do, but my 3 cardinal rules in the other posting linked above will apply to you too. 
Whether or not you use the extra Flow brood box will depend on whether most beekeepers in your area use double brood, or just a single box.