The material used is the same pink foam I have used for all by building projects. The sheet is 40 mm thick, quite easy to cut, rasp or score, will take standard household paint nicely.
The template I use is laid in a grid pattern (base width) for the maximum allowable size terrain feature for DBA. For hills, woods, fields I prefer a larger piece either 3 BW x 6 BW or 4 BW x 5 BW. This castle like the fort I built will fit a smaller area of 3 x 3 to allow placement on a hill.
First step is to cut sections out. I am not worried about dimensions as these blocks will be trimmed down to allow an interior opening for an element. As you will note from the photos, the structures did vary in height and this model will copy that. The tallest fixture, the tower, should not be more than twice the average height of the model, less it be knocked over during a game.
At this point, all cutting is done with a simple bread knife. Score the surface first before making your cutting strokes. In the last photo, all blocks are nice trimmed and squared off. The shavings are saved as these will be useful later.
Next, giving shape to the blocks.