I'll try and post some pictures of my place, my concern is that these pieces would become airborne when we have windy conditions or the rogue gust and end up in my living room, the back of my house where the wood's stacked is mainly glass.
Screw the tin on the corners and then pick the wood from the middle until you feel the need to lower it.
Or you can just throw green uglies on top/ tie bricks with rope drapped over the top etc. If it blows off your stack it's gonna go ~3ft unless you have a tornado or hurricane and the tin will be the least of your worries.
They also sell some vinyl stuff as well. Either way someday you may decide to build racks and then you can secure it permanently.