You probably don't need an entire roll....I change mine every 4-5 months, so use the roll. Look in the "filter" section of your favorite hardware store. You'll find pre cut filters. Good luck w/ your home made cabinet!!! KUDOS!
Thanks for all the advice Aridbud. I'm ordering 3 120mm fans and carbon filter roll from Amazon.
Soul...go larger for air flow.
Joe.... Grow neutral or not quite stinky strains indoors. Save the aromatic for outdoors.
Yes, I've been pleased with results....changing out carbon/charcoal sheets do make a difference!!!