This is an awesome Enderman Xp farm that works in minecraft 1.11. You can get many levels of Xp and stacks of ender pearls.

Step 1:

The amount of resources you will need depends on the amount of levels yo want in your farm. The more levels you have the more Xp you can get.

Step 2:

You will want to make a bridge about 250 blocks long straight out any direction from the main-land. It can be made from anything but using upside-down slabs prevents endermen from spawning on the bridge and will increase the efficiency of your farm.

Step 3:

When your bridge is about 250 blocks long you can start on the farm itself. Create a platform that is 2 blocks wide and 15 blocks long. It is a good idea to light up the platform to prevent endermen from spawning.

Step 4:

From the top of the platform you will want to pillar up exactly 43 blocks. If you go up too many or not enough either all the endermen will die when they they hit the bottom or they will have too much health to be able to kill them with one punch. When you are at the top you will want to make a rectangle all around the platform at the bottom. Don't fill it in or the endermen wont be able to fall to the bottom

Step 5:

On the inner part of the rectangle place button all the way around. Then build two more layers above that and on the inside put vines above the button.

Step 6:

Now place one more layer of blocks on top of the rectangle and build out 4 more blocks on each of the long sides and one more on the ends. Place pillars two blocks high on the edges where the center hole is and on each of those place a tripwire hook and connect each opposing one with string. Then go two blocks over and one block up and place sticky pistons facing inwards on each of the blocks. On the faces of each piston place a solid block.

Step 7:

Place a redsotne line from each of the tripwire hooks and run it around the outside of the layer. Then alternate between redtone and a repeater behind each of the sticky pistons. The pushing mechanism is now finished.

Step 8:

You will now want to fill in all the blocks around the pistons and above the bottom layer to prevent endermen from spawing there.

Step 9:

Go up one block and repeat steps 6, 7, and 8 until you have as many layers as you want. The more layers, the better.

Step 10:

Once you reach the highest layer you want place pressure plates on the top layer to prevent endermen from spawning. When you are finished that, go down to the rectangle you made and starting two blocks up place a layer of blocks on every second level to prevent endermen from spawning.

Step 11:

You can now decorate the bottom of the farm and the bridge using whatever blocks you want. It is a good idea to add an enchanting table and anvil for enchantments. Adding chests is also good for storing extra ender pearls that you collect. I hope you enjoy your new enderman farm and get lots of pearls and Xp.