A friend of mine built one that is shown in DOTO's link. It looks awesome
For my creep, I picked up a big planter at Walmart a couple of years ago with similar shape to yours. It's a dark burgandy, so I didn't even bother painting it since it looks great at night. While it doesn't have the traditional cauldron shape, I don't think anyone notices because they are focused on the creep.
I saw a hose holder at Sams the other day that looks like it would make a great cauldron but it's a little pricey.