A dialogue script would be a homage to the ancient Greek philosophers, as epitomized by Plato. The simple dialogue script would include setting information for each scene, and lines of philosophical argument from each speaker. Very little non-philosophical dialogue occurred in the Greek dialogues, so a script based on this form should stick primarily to argumentation. You could base a dialogue on the pre-Socratic philosophers or Plato's works, or it could be completely unique.
A skit is a short comedic scene. A skit on ethics should end with a serious message, because ethics is a serious topic. A skit consists of dialogue and setting information. Skits may also involve some slapstick comedy.
One-act plays are brief performances consisting of two or three scenes. A one-act play on ethics could deal with virtually any topic. The difference between a one-act play and a dialogue is that the former has dramatic action, whereas the latter only has argumentation. A one-act play on ethics would develop the message through a story rather than through explicitly stated points.
Film scripts are much like performance scripts, except that they do not contain setting information that would be inconceivable on screen. Film scripts do not contain instructions like "exit stage left," because such information is unnecessary in film. In film, you can develop ethical themes through argument, plot, and visuals. A feature-length script on ethics would be a great idea for a final project in film school, but would probably be a too much of an undertaking for a philosophy course.
Monologues are scripts featuring just one speaker. A monologue is different from a speech in that the speaker assumes a fictional identity. A monologue on ethics could have the speaker assume the role of a famous philosopher, or could involve the re-enactment of a famous moment in philosophical history (e.g., the trial of Socrates).