How to build a windowsill herb garden in a small space?

Do varied height and diameter glass containers,

If you find a shelf slightly deeper than your sill, screw it or Velcro to your sill.

The only thing that I have seen.. that looks like it would work in a small space... and survive to produce well... is one of the AeroGardens... and they are expensive..... consider putting in a herb garden outside on a porch or patio.. in a container.

Window Box and Pots of Herbs.