MGP10
90x45 70x35 untreated pine https://www.bunnings.com.au/70-x-35mm-mgp10-ut-pine-timber-framing-1-2m_p8030006 under structural timber
1800 x 900 sheet of flooring under structural flooring
https://www.bunnings.com.au/16mm-standard-mdf-1200mm-x-2400mm_p0590059
https://www.bunnings.com.au/18mm-standard-mdf-1200mm-x-2400mm_p0590060