I thought because some pallets are treated with chemicals to prevent rot and bug they were not safe to use? It rains here a ton and if it's true Id hate for the rain to leech out the chemicals and kill one of them!
I am going to use ikea storage shelving units turned on their side for mine. I have not built it yet but I think it will work well. Obviously you have to add plywood and other stuff but the shelving units should provide a nice frame ...