Thanks for all the kind words folks...
There is a detailed description of all my work above, but with all the old images reduced to thumbnails it's a bit hard to follow. So rather than just repeat myself - and with apologies to those who have seen it all before - I will do a few edited 'highlights'.
The base was made using a off-cut of insulation board - the sort you can find for free on most building sites.
The farmhouse is a style which was quite typical for the Ardennes region at the time. Mine is a composite of various real buildings which I found on Google Maps by using Streetview and looking for interesting old buildings. Once I found one I liked the look of, I would choose the right angle and take a screenshot.
For example, this one in the town of Warch:
The front has been rendered, but the gable end shows the bare stone which is how it probably looked at the time of the Ardennes Offensive. I also decided to drop the gable end because this is another distinctive part of the look of these Belgian farmhouses.
Once the Approximate size and shape of my building was worked out I replaced my rough-cut version with a thick card template (as seen at the top). This was then used to cut out the high density XPS foam board that I used for the walls.
Once they were cut to shape I scribed the stones and bricks using a knife, then widened the gaps using a toothpick.
This enables you to make any shape and style of building and - most importantly - one that looks unique. Eventually, I ended up with the finished structure like this:
The walls would actually be thicker in real life, but although I had thicker XPS board, it is much harder to cut accurately - especially around doors and windows. This can be disguised when putting in the window and dor frames anyway. The visible seam line at the corner will be covered by a drain pipe...
The roof tiles were made from thin card cut to shape using a guillotine and laid one-by-one using UHU. This is slow work, but worthwhile in the end.

And so, in the end, I ended up with this before any filling or painting:
More to follow...