First off, describe exactly what you want such as:
Voice should get louder near the end and the "HUNGRY CAST!" should sound like the guy from those monster truck rally commercials.
If you want pauses or other mechanics, then indicate them. Specifying music or no music (sometimes called dry or wet) is important. If you want music, you probably won't have to supply it unless you want something specific. A voiceover pro will have tons of soundclips lying around just for this use.
It also helps to verify the file format that you're going to get. I prefer very high wuality MP3s or WAV files. I know that I'm going to compress them further when I encode my show so I want to start with the highest quality stuff I can.