I'm not quite sure how it would work. I can see it going horribly wrong if every one works on the same bit. I was thinking more like, we have a layout and people add and take bits from it until we settle on the BEST LAYOUT EVER, then we work playtest it to oblivion then work on decorating bits of the map.
We should do this, it could be a little be of everything that just flows naturally. I think if we base it off of the wilderness (i.e. veitnam, iwo jima) with tunnels that go under ground, and secret hidden holes, trenches etc. We could even have random spawn points so that way it would be unpredictable and increase the intense amount of gameplay. Weapons can be lined around the map in different areas (for example the para could be in a bunker, and rifles could be in the trenches)