You can use Dia with its available elements to draw a shape and then export it to a shape file, by using File (of diagram)->Export->By extension->Shape.
But until now, this shapes don't have any text box. (They are expected to manage some svg:text but not a text box). If you need one, you can edit the file.
Together with the shape file, you get a png file (after accepting the proposed size) which can be used for the shape's icon.
By using File(of principal menu)->Sheets and Objects you can create new sheets; and add, remove and parcially edit shapes; and copy or move shapes from one sheet to other.