Not to be funny; I'd buy plastic. I think all metal will oxidize over time: brass, and copper to some extent, turn green (they call that a patina); iron turns red and is way faster (they call that rust), even aluminum will oxidize but at a very slow rate. Why not a redwood trellis for your roses. I would not buy a cheap one that is stapled together - make your own, redwood slats are not very costly. My 2 cents.

Robert

My old galvanized watering cans last for many, many yrs & I usually buy them used! I agree 'redwood' for your lovely roses. Jeanne S.

Plastic ages and cracks. I had some plastic watering cans, but the did not last and they got all clogged up. I use rubbermaid dish basins to move soil around and the plastic does turn brittle and crack. I have never cracked a plastic watering can, but they were just a real pain to have around. They were ugly and cheap looking. Due to the exposure to sun and temperature change the molecules of plastic will begin to breakdown over time. I assume this would also hold to plastic sheds. I know plastic compost bins will crack in ten years time.

Steel will definitely rust. Galvanized ones will last a long, long time. Brass is very soft and easily dented/broken and copper will patina, which, if you like that will do well. I actually prefer plastic watering cans, but I don't buy the hard plastic ones with long, slender spouts. I buy the ones that are the same design as the metal ones, but they are a softer type of plastic. I tend to drop mine a lot and/or sling them around in the garden while working...hence the plastic ones. The one I currently have is about ten years old.

It is very hard to find out what to clear metal with. If it is just metal you have use one thing, but if it's painted metal you use another. I bought something on eBay and I am not sure if it's metal or painted metal or some kind of coat. So, I wanted to clear coat it.

Of course I have problems with thing like garden trowels also. I had a steel one, it did not rust but something happened to it from soil contact, I guess. It still works, but does not look very nice. So, if something looks nice like a metal animal say like a garden frog, you may want to clear coat before leaving it out in the rain. I don't know I don't have any of that kind of cute garden animal junk.