Hi. I very happy with my design. I sloped two sides of my 8'x8' bin. The first year I did not do this and like others, I had a lot of coal that could not be burned. Some mornings there was no heat in the house because the worm was exposed. No coal was rolling down to it. Very frustrating. So I errected 3 4x4 post in the three corners and ran 2x4s standing on edge across the bin. Then I installed 2x4s like rafters sloped down to the auger. My slope is around 45 degrees. I can get 3.5 tons of coal in the bin. Maybe 4 tons if I raise the one wall a little bit. This design has made burning coal very very easy. I don't have to worry about the aforementioned.
Also, this past year my worm broke. Since I had the dog house (as efm calls it), I was able to replace the worm without touching one piece of coal.