Well if you look at the Jib on the website, its basic construction is simple. A tube, welded to its base plate with ample gussets for support, with a similar setup invert on top. The top tube will need to have an ID just a little bit bigger than the OD of the bottom tube. This will allow it to slip on, and rotate. Too tight and it will bind, too loose, and it wont keep you boom horizontal and will diminish strength. As for rotating, you could find a thrust bearing about the diameter of the bottom tube and include that to help the rotation under load. You would probably need to cap the base tube, and attach the thrust bearing to this cap. Then depending on the type of bearing, you may or may not have to attach the top tube to it. You could cap the top tube with a larger square that could also serve as a mount for the boom. Again, use substantial gussets on this cap to help stabilize, and support the load on the boom. Use a simple heavy gauge I beam for the boom, and make sure to put a stop on each end to limit the travel of the trolley...you wouldn't want it falling off under load! When picking you boom length, make sure the I beam is capable of supporting the max load you want to lift at the end. If your materials are not heavy enough, someone or something is going to get hurt!