Thanks chaps

A quick mention on the height of the tiles.
I glued the 6mm MDF to battens to add some height for basements and the such like. The Sydney Roundwood blog has a great series of articles on building a damaged WW1 village:
http://sidneyroundwood.blogspot.co.uk/2010/04/planning-fortified-village.html?m=0His church has a crypt and so will mine, though unlike the basements of my houses it will have survived the bombardment. Inspiration for a crypt also came from Jimbibbly's terrain for the BLAM15 Dorsetshire smugglers game:
http://leadadventureforum.com/index.php?topic=70094.180That the boards are on plinths also gives me the below ground space for electronics such as LEDs.
Why then the additional layer of 5mm foamboard? This is there for a small drop in level when I start on the tiles for the open countryside. Basically, I want the cobbled road that leads into the town to be a little higher than the surrounding fields. That the field tiles will also be on battens will provide the depth for ditches, ponds, etc.