First of all I cutted some 5mm MDF and 5mm Depron in tiles of 25cm x 30cm. Then I drew a 5cm x 5cm grid onto the Depron tiles, marked those areas that will be massive walls and cutted these out. Then I glued the Depron tiles onto the MDf tiles.
Here you see the grid and the areas that are marked as walls (with that diagonal line)
After cutting out the areas and glueing the Depron tile onto the MDF it should look something like this.
Don't throw the cutted pieces of Depron away! You need them again later.
You can see the tiles are not too massive but still durable.
The second step is to cut out the wall pieces you need for each tile. I decided to make the Walls 6cm high, this is enough to overtop an Ogre but not to high to play inside the corridors. Because of the grid drawn onto the Depron a wall section is at least 5cm wide and you can easily calculate the measurings you need for your walls. So now just draw them onto thicker cardboard and cut them out.
When cutted out all walls you should have somthing similar to this.
For additional detailing I use those industry parts. (forgot the manufacturer)
Most people would throw this stuff ritgh away but for building a Bunker Board those parts are priceless.
Next time starting glueing the walls onto the MDF/Depron tiles.