Last night, I was messing more with the automatic rules for placement in the region editor. I got it so it determines if a tile is considered flat or not (there are some minor bugs). In the following picture, the blues are places you can put a tile, red are too steep for a tile.
I also started the scenario editor. The first part of the scenario editor is placing of buildings, this is also used in the game. At the moment, I'm going to just create a "plate" at large as the building being placed and let the player see where it can or cannot be placed. That should give me a good basic start on this entire process.
Ideally, when you move the mouse around (while holding the spacebar at the moment), it will move the plate around and turn it blue when you find a valid spot. You can rotate with the right mouse button. However, there is a little bug with the Irrlicht.NET CP code (that will be fixed as soon as it gets into SVN, I think) that prevents me from finding where the mouse is over; that should be fixed "soon.' and I'll be able to move forward with this.