What was the Roman vernacular? (Spoken Latin??)?

Any Latin scholars around? I read about Vulgar Latin (wikipedia and such) but have found no grammar or examples. Is this info known? I am incredibly interested in the Latin language and the Roman Empire. I'm working on a musical project in Latin and have a song from the standpoint of a Roman peasant. I wanted to write it in more of a "Vulgar" kind of Latin but can only find next to no info. Mainly interested in the language that was spoken by the common people of Rome. Thanks!!!!!