The key to making a great base is three simple things lots of cobblestone,plenty of water,and a good amount of obsidean.First you have to make large cobblestone walls about ten blocks high then skip two blocks up to build a roof.Once you have done that you must build an obsidean porch all around the tenth block all around the base do that two more times after that.Now what you hast do is put water all along the first block of the porch to protect from all TNT cannons be sure to claim some just outside the base so people don't get on top of your base.Lastly you have to put water all over the top of your base be sure not to let it fall off the edge of the roof do to the weird water physics this should be done very quick.Now your base should be completely raid proof.