Here are four large recycled planters.
The first started life as the end of a large propane tank. It is about three feet across. To salvage them, they cut off the ends and split the body. So it's about 1/2" inch mild steel. Very easy to drill for drain holes. It sits on a piece of steel pipe from the oil field steel yard.
The second and third are former satellite TV antenna dishes, the solid kind. The second one sits on a concrete ring made for a waste water conduit. (You need a lot of strong friends or a loader for these.)
The third, another satellite dish, sits on a retired stock tank.
The fourth is also a propane tank end, but this one is five feet across and sits on a piece of steel pipe. This planter has gone to seed, because it is set for complete overhaul, moving the agaves out, evicting the Buddha and turning it into solid plumbago.
The agaves really seem to love the shallow sandy soil that dries quickly and stays dry much of the year.
(The flower" in #2 is one of three in a cluster. The stems are steel rods with "leaves" welded on. The blossoms are metal street sweeper brushes with some color added.)