For the past 6 years Kapcon has been running a scenario design contest. The challenge is to write a 3 hour con scenario (usually including pregenerated characters) which could be picked up and run by a GM at Kapcon with minimal preparation.
Usually, people who write SDC entries also run them at Kapcon, but you don't have to. In fact, you don't even have to come to Kapcon to enter the competition!
Examples of previous entries can be found at http://www.sdc.rpg.net.nz, the website of the scenario design contest.
Entries are due in on the first Monday in December, so if you feel like entering the sooner you can start writing the better!
More details available on the official Kapcon website.