Adding a Custom Map to Dreamball
Dreamball makes use of the Bonus Maps UI for implementing custom maps. See the Bonus Maps page for a more in-depth description of using Bonus Maps. Once you have finished and packaged up your map find some File Hosting Sites and release your map! Be sure to show it off on the Dreamball forums for everyone to see!
Note that the Bonus Maps UI is only for singleplayer maps. If you're making a multiplayer map just launch it via a server like any other Source game.
See the Dreamball Dev Kit/Bonus Maps/ folder for an example of Bonus Maps usage if you need it.