Here it is, after I've opened the front panels, and taken out the first barrow-load of wonderful compost:
This set of bins (built by me, from leftovers, about six years ago) are each roughly a yard deep, a yard high, and two yards wide. We use them in rotation: first we fill one, re-filling it as it sinks: when it gets to be higher than the sides, we start filling number two, leaving number one to rot.
In this garden, I have an old doormat that I lay across the top of the "filled" pen - not to keep in heat, or keep out water, or anything like than, but purely to remind the gentleman of the house not to put any more grass clippings on it!
If all goes well, he spots the mat, and his grass clippings go into pen number two along with all the garden waste, until that one is also full right up to the top.
At this point, pen number one is usually down to about half height, but it's important to leave it to rot, and not to add any more to it. Instead, we move on to pen number three, filling that one, and leaving number two to rot.
This is the danger point - I have to move the mat to pen number 2, leaving number one open, and trusting that Mr Client will remember not to use it!
By the time number three is about half full, number one is ready for use: if the very topmost layer hasn't quite rotted through, it gets tipped into number three, and the rest can be used on the garden. If all goes well, the pen is emptied before pen number three starts overflowing: at that point, the cycle moves round one step and we start again to fill up pen number one.
I always advocate building compost pens in threes: I never, ever have to turn the heaps (a back breaking job I am happy to avoid) nor do I have to "stir" the heaps: they are practically no work to maintain, other than moving the mat across.
And if you want my "trick of the trade" for compost bins, it would have to be "don't ever make a pyramid".
Always spread out the waste - in fact, if anything, make a slight hollow in the centre, so that any rain, including dew, runs into the heap, not out of it. More compost bins fail from being too dry than from being too wet, I assure you!
I never bother with carpet covers, or lids: I find that they process the waste perfectly well, if you leave them open unto the sun and the rain.
I often get clients telling me that their compost heaps "didn't work" until I came along, which always mystifies me, as I don't do anything special to them.
I do, however, offer a lecture on Composting and Leaf Mould, so if your gardening club or social group would like to learn how an expert does it..... give me a call!