My stacks are top covered with tin roofing sections that were given to me by my wife's uncle (leftovers from his construction company). The sections are 10 ft long and I've just layered them over the bins that hold my cords. They are held down by wood screws as well as heavy odds and ends wood pieces that wouldn't fit good in my stacks. The wind (esp this year) has been a real PITA and I've had sections of roof come undone more than once, hence me adding the heavy wood pieces. I think I've finally got it to where it can't move, had 45 mph gusts over the weekend didn't seem to budge. I also notice with how I've placed the tin sheets over my bins the rain seems to run off the sides keeping the stacks dry. Heavy rain in the wind the wood is going to get wet no matter what and that's ok with me.