Evaluate the physical properties of potassium, magnesium, and copper. Select the best choice to use for a building project. Why is this metal the best building material to use?
Well, copper is commonly used as a roofing material.
From this site.
You can see the verdigris, the copper oxidation product, in the given image. That's a beautiful old house.
On the other hand, both sodium and magnesium metals would rapidly oxidize with water.
Sodium is a good deal more active than magnesium, but magnesium would also corrode pdq. Magnesium sheeting would also pose an unacceptably high fire hazard.