I needed a round lid with a hex pattern in it. I have previously published a parametric square pattern that i coded in scad. You can find it here: http://www.thingiverse.com/thing:476127. Rather than just dumping the square pattern in an stl file and cutting it in FreeCAD, I decided to code a new version of the pattern with a nice round border.
Open the Customizer and enter your specific parameters to create your own round pattern.
For whatever reason the Thingiverse Customizer often fails to load for me. If that happens you can download OpenSCAD from http://www.openscad.org/ and use it directly on the scad version of the model. OpenSCAD is a breeze to install and is much faster than the Customizer. Another option is to switch browser. I have had better luck with Firefox than with Chrome.