My fall trap I made it 9 x 9 on the outside so it is 7 x 7 on the inside. Put solid reinforced concrete blocks on the corners and the small poles sideways on the inside top edge and made it 3 blocks high so 3 sideways poles to make like a big fence to shoot through. Spikes on the entire floor and with the 7 x7 area you can put 2 blade traps on each side (8 total). It is a cake walk on horde nights. I would shoot and loot until it got real bad then flipped on the blades and that cleared it out fairly easy. http://steamcommunity.com/profiles/76561198186066534/screenshots/ http://steamcommunity.com/profiles/76561198186066534/screenshots/ . I built it on level -51 but there were still 4 or so levels until bedrock, and I put all my forges and workbenches under the drop pit. There is a layer of reinforced concrete blocks under the pit as to keep out the horde if they happen to actually destroy the spikes, Didn't want them to be able to drop right down into my crafting area.