>A few notes on the mechanics: The way I would do it is have a wall construct from one wood and one fortification material (wood, stone, take your pick). One nice feature we could add on top would be to change the type of fortification afterwards. We could probably throw that in with repairing: You need to bring a fortification material in order to repair your wall, and if it doesn't match the material of the wall, it changes over after full repair.

Sort of like this. Also the external features from your concept like drawbridges , nice thoughts.

>The Hammer

The thing is, that I searched for an alternitive for flints for the scenario start. A pick would be my second guess. Without another tool, it's still possible - but more flints will be needed at the begining.