what to build?

make a tree house and pad the inside and see if you can make it fall out of the tree
 
Second the guard tower idea, if there's no chance of a trebuchet. Probably better to make it of stone blocks. Probably best to get a crossbow for it, bows are a little harder to work, or both if you want.
 
it would be cool to make a mini catapult. like three feet tall, mount it on the guard tower, right next to the crossbow, and launch fireballs. thatll teach people for being near my house
 
no fire balls....extra large spit balls.
 
super glue
 
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