Chris, I have no idea how to make carbon from scratch. I looked at Petsmart for the carbon and it was more expensive. I got mine at Petco, its a store brand.
For me this way was much cheaper. I wanted to change the carbon on 3 filters and the price of a 3 pack was close to $10. So I bought the loose carbon instead for $4. If I only had one filter to change media in, then I would have just bought the premade stuff.
Doing it this way, I can cut a piece of sponge filter off the big pad, and change the media around as I need to. In the long run it is a whole lot cheaper. Not as neat and tidy looking as the premade, but all those are is a pad attached to a plastic frame, and carbon in a mesh bag. I just stuff the sponge into the filter where the water flows out and the carbon bag behind that.
When I change the pads during a water change, I will take my filter to the sink, squeeze the gunk out of the old pad into a bowl of tank water, then soak a new pad in that while I clean the plastic parts of the filter. Then put it all back together. That way some of the good bacteria gets into the new sponge. I usually change the carbon when I notice the water not as clear or I start to get the "fishy" smell.
Acer, Yeah, I sewed little bags together with the netting stuff (its a pain too!). Then used a funnel to pour the carbon into them and sewed them shut. I think it took me 30 minutes at most (I have a sewing machine)Then I just rinsed them off to get the black dust off and replaced the bags. You could probably use the feet of nylons too and just tie the open end closed. You could probably get the knee highs at a dollar store. It just needs to be something the water can flow thru. You can also buy premade netting bags at the pet store for like 89 cents for a small one.