I'm in the middle of a similar project with my 7th graders. We started out by exploring Eric's World of Humanities which, if you haven't checked out yet, is definitely the place you should start. Students chose a civilization and thoroughly explored it, putting together the different facets of a civilization. After that, we jumped into the main phase, wherein students create their own civilizations from scratch in survival mode.
I split the kids into teams, then assigned each team an island with a different biome (desert, mountains, forest, swamp, wintery place). Each island is heavy in one resource but very limited in others (lots of wood, but no metal). They then had to use the resources available to them to a) survive and b) create their own civilizations meeting the requirements established during the World of Humanities period. I've attached the handouts we're currently using, if those can be of use to you.
Next week the kids start trading with each other, and I plan to record the process, so I'll let you know once it's up on my blog.
Dan.