And a hardy welcome from a fellow Iowan!
I googled this at one time and did find some instructions -- just don't remember where. If I recall correctly, they were using two 4X8 sheets of plywood, mounted side by side, painted with multiple layers of paint. If it were me, I'd also finish off with several coats of some type of clear waterproof finish. You know what the weather in Iowa is like. It will take a beating out there!