OK first dig a 5 by 5 square.make sure it is 2 blocks deep.
next,place redstone all over the bottom
Then,do /give (your minecraft name) 137.that will give you a command block the find the middle and place it there.then right click it and type /say ssssssssss.make sure redstone leads to it or this wont work.
after that,place TNT in in the 5 by 5 make sure redstone can activate it.
then find a place to put a chest and put gun powder in it
cover up the 5 by 5 then put pressure plates above it.
then build a fake creeper.
and steep on the presser plates and you are done.

i made this one because i wanted to make my first one a BOOM!!