Step 1: Design 3D model and decompose into panels
With the model in hand, we use Rhino (available as a Work In Progress download for Mac) to unroll "developable" surfaces which lie flat and can be sewn together into the original model.
Next, we need to add 10 mm seam allowances and arrange the parts onto printable pages. Using Illustrator or Inkscape, we can take the DXF output of Rhino and use 'Path Offset' to add seam allowance. The panels with allowances can be arranged manually to fit on printable pages. This method works well but can be really tedious with many panels.
As an experiment, we read the output of Rhino and programmatically added seam allowances and nested the parts on paper stock.