That's how it should be! => (그것은) 그래야 돼(요)! => (그건) 그래야만 해(요)! There might be a more specific phrase if the context is known. Basically, 그러하다 means "It is so" or "(That's) how it is". To add the sense of "should" or "must", you make it "그러해야(만) 되다/하다", which shortens to 그래야(만) 되다/하다". Adding the subject "That is", it becomes 그것은 그래야만 돼요, but the subject may be dropped if it doesn't refer to anything specific. 되다, the base form, transforms to 되어요 when it comes at the end of a sentence, which then shortens to 돼요.

Personally I would probably say 이/저/그렇게 야돼요. If it is natural or even grammatical, that's another matter ㅋㅋㅋ I guess perhaps it would be more like "it should be like that" ^///^