Thanks for all your nice reactions.
As some of you have suggested, the master plan is indeed to build a minifig-scale version of Minas Tirith. I have investigated what this would mean: the outer diameter would be about 10 meters and the height of the central rock would be 6 to 7 meters. It would contain a thousand houses. A daunting task indeed...
If I were to build Minas Tirith at the same scale of this seventh level, it would be about 1.5 to 2 meters diameter. Still far too big to manage.
I have a plan to build a version to fit on four 48x48 baseplates. The rock should be about 60 bricks high. That is the biggest I see feasible for the moment. This size only allows room for 4 levels. Still, I imagine that the look and feel of Minas Tirith could be nicely recreated.
I will need more bricks however. After the current MOC, i have exactly 12 white bricks left....
For the next few MOC's, I plan to build some city parts separately. My ideas include:
-main gate, with the battering ram Grond
-a section of the wall, with an orc-filled siege tower
Any more ideas?