Use Rectangle to create a closed box shape with 4 control points, you can define the width and length of the box. You can also make the box have rounded corners by changing the fillet example, this will add an extra control point per corner as seen in the pic.
Rectangle Param Description
Length
Length of the box (Z Axis).
Width
Width of the box (X Axis).
Fillet
How much to round the corners.
Rectangle Class
public class MegaShapeRectangle : MegaShape
{
public float length;
public float width;
public float fillet;
}
{
public float length;
public float width;
public float fillet;
}