In Oral Interpretation, you can basically perform any piece that’s published, but it’s best to avoid doing a dramatic piece with many characters for one reason: pops. If you want to perform a dramatic piece for prose, I would advise against doing a piece with many characters because the pops can be overwhelming if you are holding a binder. Shifting between two characters is fine, but many more than that will just water down your performance and make it hard for your audience to follow the piece.
Of course, there are ways to get around this, such as making your binder part of each character stance – raising it slightly and keeping one hand on it as one character, holding it lower for another character and letting the other hand rest by your side – but in general, it’s best to use prose pieces that have just one or two characters.
A great way to get away with doing pops in prose is to coordinate the character transitions with your page turns. For example, if you’re performing an epistolary piece – meaning that it is written in/you are interpreting it in a letter format, with one character reading a letter to the other and vice versa, try to fit each character’s separate speech on a separate page. That way, you can read one page as one character and then transition to the second character while you are turning the page. Keep in mind that this advice pertains to dramatic prose pieces. If you’re performing a humorous prose piece, by all means, transition with character pops if at all possible!
It really adds to the energy of a humorous piece and will allow you to have some fun with your physical interpretation of the script. Again, you can even make your page turns part of the performance: If you’re playing a loud, energetic character, flip the page dramatically. If one of your characters shakes or wiggles throughout the piece, translate that action to your page turns as well. Don't forget that you aren't allowed to use your binder in a way that might be considered a "prop."
At one competition, I saw a girl pantomime blowing fairy dust on her binder and opening it dramatically to begin her piece, which was about fairy tales. That probably wouldn't cut it in most districts... Check out this post on Making Page Turns Work For You for more: http://www.forensicscommunity.com/poetry/making-page-turns-work-you