This tutorial will teach you how to build massive structures fast (With precision)!

Step 1. Make a server (Or go on one that has it pre-installed), install a permission area plugin. Make sure you can place blocks!
Step 2. Protect your area, making sure that the area you want to build isn't protected (I prefer doing 1 side at a time)
Step 3. Build you wall, you can place random blocks everywhere and the blocks that are in the perm area will be removed and a message saying; you do not permission(s) for this area) Remove the protected area once done. You may want to disable the chat bar as you will be spammed by the warning!
Step 4. Look at your final product. Could potentially work for non rectangular/square areas!

-koh1998