You're not going to be able to find a single example that exemplifies all the various concepts that are typically rolled into the term self-organization. To find an appropriate example for your use case, you need to decide what specific behavior you're trying to model.
What Your Example Models
Nobody tells anyone what to do – everyone pitches in to do some part of the clean-up until it is all completed.
I'm not sure this example communicates anything beyond "you're on your own." Yes, I can see how you can retcon a theme of self-management around the convenience of having people clean up the conference room, but I don't think it sends the right message.
The actual behavior you're trying to model with the example you provided is:
- Individual initiative.
- Lack of prescriptive command-and-control.
- Bottom-up planning and execution.
These are certainly aspects of self-organization, but none of these things really highlight the collective ownership that you say you want to model. You need a different approach.
Model "Collective Planning" Instead
In my personal experience, the concept of collective ownership is best modeled through Planning Poker exercises that are stretched to include all members of a cross-functional team. For example, you might use a login-page story and encourage the team to stretch the development story to include technical writing, database architecture, or network topology to show that the whole team needs to be part of the plan and execution.
Model "Cross-Functional Participation" Instead
You might also consider trying an exercise that requires every member of the team to add value to a story, in order to show that a story can't be completed without the participation of the whole team.
For example, you might give everyone on the team a single facial feature for Mr. Potato Head. Everyone adds value to Mr. Potato Head by adding an eye or an ear, or ensuring that parts are in the right places. By passing the head around a circle, you model whole-team participation in the definition of done.
NOTE: You might be tempted to try to make this particular example more more free-form in order to model the communication necessary to swarm or self-organize around a team-developed solution, but in my experience the task is both too prescriptive and too simplistic to make that point effectively. Your mileage may vary.
Use Multiple Exercises with Inspect-and-Adapt
Self-organization is a surprisingly complex concept to communicate. Each exercise should clearly communicate an individual facet of this concept. As a corollary, focusing on facets of self-organization rather than the gestalt may require you to use more than one example to illustrate your points, and to iteratively refine the team's understanding over time.
Feel free apply Scrum's "inspect and adapt" concepts to your team exercises. If you have a point to make, use a review or retrospective of the exercise to make sure the point was communicated effectively, and set the stage for improvement of future exercises.