It's going to be 3 "parts", and then an infinite panic event in the end. Each "part" will consist of additional two halves: in the canal, the short & dangerous route, or a detour, a longer but less dangerous route. There is an issue however, the engine limits. I keep wondering if such a long map would be possible, never mind with all the scripted events and alternate paths. Worst case scenario, it will be 2 "parts" with alternate paths, and the last one will be a single path(maybe with some smaller alt. paths), leading up to the final event in the map.
I don't want to make it too long, but I want to make it longer than the average L4D map lenght, and the longest in this campaign.
Right now I'm working on the long but safe detour path for the first "part", and there is also a small military encampment part before that, in which I plan to put a little conversation between military officials and the survivors.
Anyway, here are a few screenshots of work in progress:
