Mark them out, cut with a circular saw and use a hammer to knock the centre piece out. Assemble the seat, and paint. Plant the garden keeping plants at the same depth as they were in their containers. Plants are readily available at nurseries or ask your nursery to order them for you. Most other materials are available from large hardware stores, building suppliers, or landscape suppliers.
Artificial rocks are available from landscape suppliers.
It's manufactured by Gripcore Aust Pty Ltd and is available from hardware stores. The post hole shovel, nail gun and most of the other tools required are available for hire. Construction by the Blitz team.