walkonable ,waterproof roof for playhouse

[woodman-46]

I am building a playarea/ small fort for my two boys at the end of our garden. I want to have an area underneath that they can go into but a walkway on top that thay can walk along. I need this walkway area to be hardwearing ,non slippery and waterproof so that no water goes into the area underneath.

I have firmly layed across horizontal "roof " joists every foot and a half to be safe and had planned on laying on top of this weatherboard and then some sort of surface that handles all of the above . Can anyone suggest a good product that would cope with this.
Many thanks in advance

James

 

[woodman-46]

Further to my question above I have decided to use 3mm ribbed rubber matting and adhere it onto the board underneath. Waterproof and grippy as well I hope.
J