This is what they look like laid out. Praise the gods, the wife had a whole bunch of interesting colours that I could use for this project.
I'm planning to use all the white tiles in the photo below to do the walls between rooms and corridors. Perhaps slice each white tile into 3 pieces to create thinner pieces? This should space the board out a bit more, and avoid the overcrowding that can happen on the original board.
The biggest thing stopping me from going ahead with this was that I wanted a board that would still be compatible with all the cardboard expansion tiles. But after laying them out on top, I think I can make it work.
With some figures set up;
A few closer pics of some of the tiles. As you can see the model bases are slightly larger than the marble tiles. This shouldn't be a problem as there will be filler between them to hold the whole thing together.