Scaffold poles, or footpath handrail poles plus MDF.
I'd have varnished it, giving it several coats with a sanding and wipe-down with tack-cloths between each coat.
But that's just me, I find plain white too clinical.
http://www.edenproject.com/shop/Scaffold-Board-Desk-15997.aspx
http://simplifiedbuilding.co.uk/blog/pole-mounted-monitor-desk/
