I am helping a neighbor build a pipe for his kid.
It seems to me that what you want in a surface is something pretty hard but bendable, impermeable to water, smooth as can be, and easy to repair if dinged.
Has anyone tried self-adhesive vinyl tiles? They are often used for garage floors in addition to the more familiar kitchen use. They run about $0.80 a sq foot, should be impervious to the elements, very hard but a little flexible, and easy to install (but installed at a 45 degree angle so you never hit the seams all at once).
As an alternative, has anyone used the white covered masonite from Lowes that is also water resistant? It comes in 4x8 sheets for about $14 a sheet.
Thanks in advance for your help.