Two chamber mob farm

A no redstone mob XP farm by moretingz, two spawning chambers pillared 124 blocks up with trapdoor floors dropping everything into a shared shaft and four hoppers into two chests. Campfires at the bottom are optional and make it fully automatic; leave them out and you kill by hand for the XP. Around 1,200 building blocks and half an hour of work, and it scales by adding chambers rather than height.

• Do not use slabs for the roof. The top comment on the video is that light leaks through them during the day, and builders on both editions back it up. Use full blocks and put slabs or torches on top to stop mobs spawning up there.
• Build more chambers. The video does two, and builders running four report roughly double the loot, with ten working fine.
• Set render distance to 8 and pillar up until you can see nothing below. That is exactly the 128 block spawn radius, and doing it that way saves torching the ground at all.
• Deep ocean is the best site, because there are no caves underneath competing for the spawns.
• Put lightning rods on top if you build it out of wood, or it burns down.
• If the water flow keeps breaking, add an extra fill block after placing the water and before breaking the middle.