It might be worth exploring if it is quicker to edit a copy of one of the built-in shapes and replace its geometry. That would save a lot of time and reduce the likelihood that you've missed on of the important parts.

In my opinion, the hardest part will be the child shapes within (each of which will have its own shapesheet) - that adds another level of complexity that makes you appreciate how long it takes to develop these 'simple looking' functionalities.

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Andrew Lockton
Chrysalis Design, Melbourne Australia