Buttons are rectangular. Design accordingly.
But I don’t understand your reference to a website? InDesign is not a web design tool.
If this is going to the web, I suggest using Muse if Dreamweaver is not your thing.
Thanks for your prompt reply, Bob. If you're wondering where I got the idea, I can refer you to an Adobe TV "Evangelist" who explains how to created interactivity in your Adobe InDesign layout and then export it as an SWF file with little further work required for it to be used as a website (and that was with CS4, so I can only assume Adobe has continued moving in the same direction). I bought Adobe Design Premium, but am not yet up to speed on Dreamweaver, Flash or Fireworks. So for the current project I was looking to do as much as possible in familiar territory.
Maybe there's a work around? There are two things I would like to have happen: I'd like each polygon to change color (transparent) upon rollover. The button could be a rectangle containing a number, which would also change color upon rollover, and would jump to a URL or open a document when clicked.
Does Dreamweaver allow you define a custom area as a hotspot and rollover? In a post about Fireworks, I saw an example posted of a map of the U.S., in which the designer wanted each state to be highlighted with a transparency upon rollover, and also to jump to a URL when clicked. They did this with a "polygon" tool.
If InDesign included and promoted these tools for interactivity, why shouldn't one use them for export to a PDF or to an SWF file? I'm assuming Muse is Adobe's latest answer to the need for friendlier user interfaces for Designers? I've spent enough money on CSDesign Premium this year and can't afford to spend more right now.
Muse is subscription only and is included with Creative Cloud.
If your goal is SWF (and please keep in mind that you will be totally eliminating anyone on mobile and pretty much killing any SEO) then it should work as a rollover.
Select the button and open the buttons panel. Then simply click the rollover state and edit the button to create the appearance you want.
That said, it will still be a rectangle.