I built 2 homemade tumbler-style composters out of large drums. They essentially spin on a shaft that has been placed through holes drilled in the center of each end. Although they are black, they are not double-walled. As mentioned, heat is a big factor and the rate of composting varies greatly over the course of the year. Worms help too. I actually need to build a 3rd and 4th drum to keep up. We put all non-protein food scraps in. When things are quick, I'll add some paper or grass clippings. I do NOT add feces and I believe I've heard it is an absolute no if you plan on using your compost for your edible garden.

This is just a photo off the internet but mine looks exactly like this except a black drum: