Examples of my work:
http://hosted.hostilezone.net/tycell/
First entry: Just abusing this space to keep some notes
(And for reference of others).
The idea is this: A TWHL community project called (temporarily for now) 'Space Station TWHL' - The simple idea is that the organiser of the project creates 2 airlocks in Hammer, an enter and an exit, then when people sign up they get given a map name, like (again an example) TWHLSS_1 When enough people have signed (my original plan was for 10, more are welcome) the organiser distributes the airlock enter and exit points. Then each mapper can make whatever he / she wants.
Now, although the airlocks are based in a space station, the map they make, doesnt have to be, they can use a teleporter to take the player wherever they like and make any enviroment, so long as they come back to the exit airlock at the end. This way its just like "I have an idea" but everyone does the work at the same time. Then when all maps are done they get handed back to the organiser and because of the airlocks, they all fit together very easily. Volla.