If I told you all my ideas, you'd might steal them. . . But anywho, Forge whatever comes to mind. What interests you? Complex Structures? Infection? Invasion? Aesthetics? Be original on your map. I don't know your Forging Style, so I can't recommend any ideas. But to sum it up, Forge what you like best, it's all about what you prefer.
oh well but any ideas that turn into maps get credit to the person to come up with the idea so everyones happy
ok forge a rail with a soccer ball on it, sloped so the ball rolls around. Then make the ball a hill, for a King of the hill game. Then build a large platform over the rail for the actual map. So then you've got this map with a hill that you have to chase after. You could do this with Infection on safe havens too, have a safe haven rolling around so that the survivors have to constantly move around the board.