There are only three rules:
1) You can only add between 4 and 8 sections on your turn, then you post what you have and let someone else add their own 4 -> 8 sections. I know it will be asked, so yes, you can add eight sections to one side and then mirror it.
2) After posting your own update, you must wait for two more people to make their own additions before making any more.
3) If you remove any sections added by someone else, they count as sections you used. If you remove eight sections, you can't add any. If you remove five, you can add three. And so on. This is to discourage people from erasing other people's work while still allowing for it.
This isn't a rule, but please try not to plan out an "end design" for this with other people. It will be more fun to let it grow out and evolve naturally. Also, please use SW-style sections. If the sections you've used aren't commonly available, please package them in a .zip or .rar. As it stands, everyone should have all of Kaelis's SW-section packs, SWA's section packs, and Squishy's converted CE-sections.
Here's the start:

http://filesmelt.com/downloader/PCS001.zip
Who's next?
EDIT: Please state that you're going before starting work on your additions, then post again once you've done your portion, otherwise we'll have several people working from the same version. First come, first served.