sheet plastic is really really expensive but that would work well. also what people do is take multiple PVC tubes and drill into them from beneath (through the wood into the pipe)
but people will be much more helpful in build-a-jib 101, and theres a lot of stickies in their forum that will help you out a lot. would really recommend visiting
ya if you want it legit get some hdpe. if not just pvc pipes or pvc siding/corner board
"one time a gaper asked if i could spinny tornado corkscrew ollie so i threw him off the chair. true story"~shmad
"No poles is like getting your dick blown by a guy. It might feel ok... but it's still gay."~Tokemon http://tiny.cc/free-karma
when i built mine i made a really good interior. had pictures but lost them. for the top i used trex which is stuff for making a deck, but i havent used it yet since i didnt get snow last year and couldnt get my summer set up this year so i dont know how well it works. next i used pvc pipe and drilled and super clued it on the side as coping. if i were you i would make it about 1ft 8 in tall cause 2 feet tall makes you need a bigger jump on to it, and also you should make it about 12ft or more cause it really isnt that big and would be more enjoyable.
get your hands on those yellow plastic tubes that go around the cables that support power lines, there a btich to flaten out but if you get them nice and flat, they slide almost as good as a box on the hill when there frozen
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