a DIY carbon filter with a computer fan...??? Now I've heard it all
I used to have a carbon filter I built myself. It worked great, but probably didn't have the most optimal flow. I had it hooked up to a 4" blower. I don't remember the cfm rating, But seriously dood, Carbon filters are cheap, I'll smoke a carbon filter in one session
I really like my phat filter. not the answer you were probably looking for. But just know that any DIY carbon scrubber will 'most likely' either not have such a great cfm rating, or not filter all that well. You can find all the flanges, and ducting you'll need at home depot obviously. some sort of sealant, and then the activated carbon. some Duh-ct tape.