This one was little involved and tiring, but worth the effort.  The mastermind behind this one discovered a very large collection of cinder blocks underneath the deck outside of the dining hall.  He recognized the potential of such a large amount.  What we did was get a few wheelbarrows and a bunch of freshmen eager to get involved in a prank.  We used the wheelbarrows to load up the blocks and take them to the doorway of the dorm.  It was quite a long trip so we took turns.  We quietly stacked them up in a long row outside of the door.  Once we had about 70 or so blocks, we open the door and formed a chain to easily move them inside.  We stacked them in front of a person's door right up to the top, making 3 sides.  It looked like this: ||____||  We put a table behind the wall of blocks and stood up a couple mattress for protection, in case they decided to push their way out.  As I said already, this one was a little tiring, but it was very creative and lots of fun.  Other things that can be used for blockading include bags of leaves and snow, provided the snow stays outside.