There's no download.
It is a very basic geometric form, take the top and bottom squares, measure their distance and it gives you a triangle for the walls.All that's left is to cut the triangle wall in half to have it match your pic.Just make a 5 min drawing and off you go.
Thanks! Sounds easy enough. Will start on it tommorow.
Dam that's cool looking
Hope you make a I'ble !
@Jayhawk - make sure you take lots of photos as you work, because that would make a great Instructable.