This Link is to a wep page that gives specific information on how to create levels in Portal 2, how you can generate great ideas for creating your game and how you can playtest your game to see if it is ready to be released into the public to play and test.
This page points you to several different sites that will help you create your own games : Platform Creator, Physics Puzzle Maker, The Algorithm Crew. and Classic Shooters
Student game created with Sploder using the 3d mission game creator. Fun multi-level game with increasing challenge and ample weapons and powerups. The game incorporates the use of puzzles to open locks. Nice job.