Minecraft wiki entry for Defense, associated text: On the surface, where you enter looks like a 5x5x4 block high house that floats, but on the inside, basically your main house is above the surface, your ditch would be one block out but 3 blocks down so that the basement of your float monstrosity can be a mob farm. It is 5x5 as spiders can jump, so you have 8 opportunities to escape from the spiders and have murder hole on the higher level to kill those spiders.