Note the routered nosing on both edges of the tread, as well as on the diagonal endgrain of each board meeting it. This is green treated lumber.

Placing the deck boards at an angle does not require any more materials if planned correctly. If any diagonal exceeds 16 ft (or 20 ft when using special order length boards), the deck board will need to be seamed together over a joist. I connect them to each other first and then to the joist after spacing them correctly.

If you don't want seams but still want diagonal decking, you will have to keep each section of deck under 11 ft in one direction. A change in height is often a logical way to do this and still accomplish a larger deck.