I wanted the diagram to be as straightforward and simple as humanly possible. So the walkway is the main axis connecting two areas, one for lounging, and one for dining. The dining area (square deck on right) is oriented towards the Manhattan view. Then over-layed onto that was lighting, bbq area.
A tricky thing about roof gardens is the allowable area that you can cover the roof with materials that are considered to be "combustible", i.e. can catch on fire. Regulations vary according to City (and year) so check your local codes. This was a determining factor in the design because the use of wood decking had to be limited.