Minecraft wiki entry for Witch_farming, associated text: Spawn Platform two is identical to the first platform. Repeat the above process. Spawn plaform three is also identical except to leave the blocks that cover the tripwire hooks off. For spawn platform three you should cover the tripwire hooks and the row of blocks above the waterlogged trap doors with slabs. Continue to the end of the spawnable area. Then, count one block inward from the outermost slab on the front of the farm and place a slab in front of that. Do the same thing on the other side of the farm. Repeat this process from both sides and you should have a two block wide overhang of slab blocks.