I use to build my filters back in late 90s early 2000s but they don't get the carbon as compacted as the store bought ones. I still have some carbon i bought off ebay way back then, i used alot of it on my aquarium filters before i got a non carbon filtration system. Store bought filters work so much better and the prices don't bother me for piece of mind.
Don't get me started on HID lights, I could have a bowling alley with how many old 1k bulbs I have sitting around. I throw nothing away grow related out of fear.