You should first look to overall AA, then differentiate between types of accounts (i.e. strategies that are highly taxed in the Roth, which has no tax liabilities, and tax aggressive in other accounts, etc.)
Often this means that an account like a Roth, in particular, won't be diversified at all (will have a large bulk of the same asset class, at the very least), but will be diversified within the context of the larger portfolio.
Is there a particular reason why you're targeting this particular AA within the Roth?