Step 1: Finding a Place to Build
Find a place to build. In my case i used one of my buildings I have built.
Step 2: Start to Build Your Base!
Second you should either make a stair case down 15-20 blocks or straight down using ladders.
Step 3: Start Mining Where You Want to Build
Now once you are down 15-20 blocks or more make a huge room for you to enjoy. Then decorate the walls and floor.
Step 4: Making It Griefer Proof
To make it griefer proof line the walls with obsidian and then do the same for the roof. This will prevent your base from being blown up by tnt and creepers.
Step 6: Decorate
This is my cake vault for a doomsday but you can design your own room.
Step 7: Optional Addition
You could also put a pool under your base and have fun in it.
Next instructable will be minecraft xbox 360! Open to suggestions.