I have built using pressure-treated timber. I'm not worried about bumping into it or hitting an occasional post, etc. It also doubles as scaffolding and standing on 45x220 feels sturdier than regular decking wood. Especially since they rest on 45x90 beams and the span is table length. I have left too little space between the beams, so an ordinary clamp won't fit, which would sometimes be useful, but at least I remembered to leave space for clamps around the entire table. This year's project is to attach some wheels so the table is easier to move; when it's wet, I have to exert too much effort to lift it myself.