NOW IN PORTAL 2! new better edition!
CHECK IT OUT HERE!---> moddb.com/mods/portal-2-memories
The idea behind this is to make an episodic mod, which you can play as it grows and every new chapter will be based on a whole new theme. The basic concept is the following:
You start at the main room. Use the portal machines to visit the chambers and gather all the eye balls. Bring them to the main room and open the gate leading to the next chapter.