Wow, Mark, that is freakin' awsome stuff!
I like the inclusion of the Mordheim plastic building bits in your buildings. The graveyard it very, very cool as well. I also like the pavement effect you have on these tiles. Very good stuff and very inspiring.
I started work on a similar project just a couple days ago. I am making 16 inch by 16 inch boards and 16 inch by 8 inch boards. To create a standard 4' by 4' area, I will need nine of the full sized tiles or a combination of full sized and half sized tiles.
The tiles are based on 1/2 in particle board with a 1 inch thick layer of pink insulation board. Buildings and other features will be permanently attached to the tile bases. With a slight additional elevation of 1/2 to 1 inch for some of the buildings, I ought to have enough depth for the occasional cellar/basement under some of the buildings. Right now I am working on cutting the pink insulation board and gluing it to the particle board base. Once I get a few of those done, I'll dig in to some basic ruined buildings and see what I can do.
I have done almost no terrain work over the years, so I really don't know what I am doing, but I figure I'll just jump in and see what I can knock out. I think once I have made some progress and taken some pictures, I'll start a thread on my project.