Here is how I built a raised bed using metal roofing materials and lumber. It’s about 28 inches high which is good for people who may need the extra height due to health reasons. It’s easy to reach to the middle from a standing position.
I don’t currently use this bed. I made it too tall to keep filled with soil. I filled it with compostable materials to start from which after the first season had shrunk the soil level in the bed by half. The plants grew fine in the bed with no issues. It was just too big for what I needed. If you choose to make raised beds out of metal roofing material I recommend going about 2′ tall as a maximum bed height.
www.GrowingTheHomeGarden.com