THIS IS NOT 3D!
Although you are using a sort of similar method of using bitmaps for the map. I think you will run into some really nasty problems in the long run.If one of your colors is even slightly not expected it will be read in wrong!
think of this not as 3d, but a 2d grid.AI and pathfinding on a 2d grid is much simpler to do than in pure 3d - where it's horribly complicated.