Add a button to toolbar/selection grid?

I am trying to make a "tab" view similar to the one in the internet browsers where you have a tab line and a "+" button to make a new button (and well, "-" to remove it), so I am trying to make a GUI.toolbar and add buttons.. But I am just confused how to do it.. toolbar and selection grids require Arrays, but it is hard to add elements to array, no? (at least I couldn't find how to do it in C#), and when I found it they said "use lists!" but toolbar/selection grid doesn't support lists.. So, how can I do it?? Also if you know a simpler way to do a tabbed menu (or an example of it) than this, it would be helpful