Chapter 12
With hex oriented modules the roof is already flat enough.
The model below has extended wall panels rotated to trapezoidal
(all except the base
and uppermost module). I like these tall models for dramatic
effect. 
NEXT
I have added the photo above next, although it skips a couple
of steps, the similarities are interesting to me. This system
includes a
three way joint and a truncated version of the rhombic geometry.
Note that we no longer have any diamond panels. The points have
been
chopped off. Where four panels used to come together (and potentially
four modules) there is now a cube or a spot for a cube. Where
there was
the three pointed panel vertex is the open triangle. And the
rhombicube that we started with is again back. Note the full
one on top of the tower.