we are revamping our robot and we made a list of new types of materials to use. if anyone has any suggestions on lighter and/or stronger materials please post your ideas.
basket siding- orange construction netting
conveyor belt spindles- tin stove pipe
We used fiberglass glazing for our sides, it was surprisingly strong and light. Our sides made it through 2 regionals and Nationals.
We (Team 926) used green garden fencing for our hopper sides. Held it in place with zip ties. Only had to replace one zip tie between regionals and championships.
We used Polycarbonate tubes for our ball collecting rollers, along with Roundthane tubing for belts. “Pulleys” were constructed by slipping short pieces of 2"OD tubing over 1.75"OD tubing and securing with acrylic weld.
We used Foam paint rollers (the really cheap ones, 2 for 1$) for our ball pickup rollers.
Team 1884 used broom heads and got 3-4 together and used those to sweep in balls at LSR.
We stereotypically use PVC pipe with lots of holes drilled in them. They’re lightweight and grab at the objects (balls, inner tubes, floppies, etc…) really well.
we used clear vinyl flooring for our conveyor belt. It is clear and relatively tough, but it tears easily and stretches. We did not have any problems with it though.
We got our rollers from 80/20. They are Al tubes with spring loaded brass bushings on each end so you can pop them in and out. (Like a TP roller) They weigh .7 lbs each for a 12" roller.
We used insect screening for the sides of our storage. It’s light, easy to install, easy to fabricate (all you need is a pair of scissors).
I almost forgot rofl. We had this ball kicker… it was a pvc that we had Lightened… because we over read the rules during 6 wk period, and so we just put zip ties in it and it fed balls to our 1st stage because our 1st stg was in the back…the kickers threw the balls twrod 1st stg… 
Get some Greenhouse material, it’s pretty much honeycomb lexan, VERY light, and pretty strong too. Teams like 173 and 1126 have used it successfully in the past, find it at your local green house equipment store.
We used sheetmetal mesh stuff… 
that was a good choice because it did what we wanted accurately…