I used trek decking for mine it is pretty cheap but if you keep your edges razor sharp they might dig into the trek like they would dig into wood. also you may want to use a power sander to make it smoother once in a while.
i remember i first joined this site because i was making a box and wanted to know what to use as a top sheet. then i used the searchbar and found like 234234 threads and avoided the n00b mistake.