Best practice for text size dimen declarations

I'd like to declare some dimensions for naming some common text sizes in my app. Are there any agreed upon standards or recommended best practices for the various res categories? Or, have there been any clever solutions for basing common text sizes dynamically at runtime on the current system default? For example, default text size is considered normal text. A smaller size is declared for minor text/descriptions, a slightly larger size for minor headlines, a much larger size for major headlines, etc.