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Materials: One 1 inch 3 sided rail 16 feet, some flat metal for the stands of the rail and someone who has everything they need and are able to weld this kind of stuff. (Friend from metal class, dad, uncle... whatever).
This whole rail is pretty much a welders job, if you can't really weld you can't really make this. First you need to cut you 16 inch rail into two 8 foot pieces, and then on each piece cut off one foot which is used for the stands.
Line up the two long rails together and make sure everything is in line. If you have some skill in welding you can weld the two rails on the top where you will be grinding and sliding and later you can sand it down. My friend's rail was made this way and it was really great. So if you can weld every foot or so right on top of the gap in the two rails then later sand it down and it should work out. If you don't have a lot of skills skip that as its not 100% necessary, my rail didn't have that and so far both rails stayed in place.
Now flip the two rails upside down (maybe one if you welded them on the top) and the open side should be facing up. Make sure everything is in line. Then find a flat piece of metal or cut of some off of your stands or what not and place one piece 6 inches from each end of the rail. This is where your stands will be. Now weld that down, this weld is very important especially if you didn't weld the top. Make sure it's really strong and it wont fall off. Do that to both plates at each end.
Now take your 1 foot long rail pieces and put one on each end on top of the plate you just welded. Weld this down to the plate, make sure everything is really sturdy, this is also a really important weld as people will be jumping on top of it and sometimes not straight so it might crack and tip if you don't do a good job. Weld this down on both ends and your almost done.
Ok, last step, take your two flat metal stands that you haven't used and weld these down really nice. Make sure they are really strong, this is another really important weld. Do it to both ends of the rail and your down. Since the bottom of the stands are metal you might have to end up taping them somehow so they won't slide around. Wax it up and skate.
I know this isn't the greatest help for people who can't weld, and I'm not going to explain how to because it's not something you do with a little house hold blow torch, you have to get someone who can actually do this with the proper equipment.