My summit pole has 3 sections that fit into each other, each section is approximately 20" long, they are very thin gauge aluminum pipe, they weigh a little of nothing. The bottom section is approximately 7/8 OD which slides into the middle pipe and that one into the top section, they are a close fit. I did not attempt to take them apart as I did not want to chance damaging anything. There is obviously a shoulder built on the top end of the bottom pipe so it won't slide out of the bottom of middle section, there must be a shoulder built on both ends of the middle section so it won't slide out of the top section, then a shoulder on the bottom of the top section so the middle section won't slide out. My description may not make sense to you, but the bottom line is that the pole sections will not fall out the bottom, they must slide in from the top section, first the middle pole, then the bottom pole into the middle one, the shoulders hold them from falling out.
I lean toward being a do it yourselfer, but in this case I would highly recommend just buying the Summit pole, it is absolutely slick. I can't imagine coming up with all the right size and gauge of pipe, finding the right size clamps, making the foldout legs and foldout pointer and it still being lite in weight and quick to use. If you are a machinist with access to all of the right material and nothing better to do, you might get satisfaction in saying you did it.