This isn't your run of the mill one type, mob trap, this trap works on all monsters(with the exception of endermen), including passive mobs and slimes(medium and smaller). This will be in projects section to properly display all features of the trap. It's proper use will drown any creatures who decide to follow you as you go inside the building. The pressure plates inside will hold the monsters out as they float up to drown, while you stay safely in the collection hole. The water will push all monsters to the inside, as they will try to escape to the outside, so this trap will require a little patience. If you wait until they are trapped, you can hit the mob to ensure experience gain, the doors will attract zombies for you, so that farm wont be an issue, plus it should distract them as you pass with ease.

link to project: http://www.planetminecraft.com/project/mob-trap-x/