I made my own years ago and it was very successful. I used an old bin with a couple of small drainage holes in the bottom (I kept a tray underneath to catch the liquid. It makes an excellent fertiliser when added to water) then 4" of gravel in the bottom, then a foot of soil then loads of kitchen vegetable waste on top. Don't put onions or grass clippings in it. I went to the local tackle shop and got a tub of red worms and tipped them in. within 6 weeks it was making composted soil and supplying me with fishing bait. I had to empty the new soil out every year but it was brilliant for the greenhouse. Don't let it dry out and keep it in the shade.