The base and fighting platform are both 3mm/ 1/8th" MDF cut to shape with my jig-saw. I got the shapes right by tracing around the top and bottom of the balsa with a marker. Make sure that there is a couple of millimetres' overlap on the top layer to produce the "lip" that you see on many vauban-type fortifications just below the ramparts.
The sentry box is just a piece of balsa rod with a half a foam ball stuck on.
The figure is a 30mm "Willie" who is standing in for the whole Turk army.