The tower was a good starting point and we can work forwards from this.
You need to think in terms of planes between the verticals and the logic of how one thing must lead to another, how the design with it's perspective 'works'. You can hear me muttering to myself along these lines in this lesson about.
Note: If a little bit of the video looks odd it's because Carrie inverted the footage she took. The result is that you can follow my carving the 'right way up'. You'll see!