I might structure the class into types of songs (folk, pop, musical comedy, country, stream of consciousness, etc.) and then go into rhyme (or not), meter, and how to work within the framework of a variety of chord progressions in each genre. Since they're non-musicians, I assume they'll have someone else to write the music? Or will actual music not enter into this at all?

For each genre, I'd bring in examples and analyze what makes them successful or not. Keep in mind that artistic and commercial success are often two completely different animals. What do they want to acheive?