First, you will need an additional FGD for hammer, the FGD plus an example map is available here:
http://www.voogru.com/files/dodgeball.rar
A few guidelines to follow:
1. Be careful not to have too many dodgeball spawners active at the same time in the map, a common issue with new maps where way too many dodgeballs spawn in such a short period of time that cause both teams to get slaughtered instantly. Be careful with the spawn rates as well, the rocket spawn time is reduced when theres more players on.
The example map is generally playable where theres not too many rockets, and there aren't too few where it's boring. Feel free to look at the entities in existing maps to get an idea on how they work.
2. Use the inputs on the dodgeball entities to properly have them enable/disable on round start/round end.
3. Health packs should always be in risky positions. Remember, if you don't let the rockets hit you, you don't need health packs now do you?
Do not use point_servercommand for anything else (I inspect the maps!)
Once you complete a map, post a thread with some pictures, if it looks like awesomesauce, we'll give it a try.