I echo Bob's comment about the shelves..That may or may not work but just remember how heavy cards are..I store all of my for sale/trade cards in 5000 count Monster boxes and this is what I use..https://www.homedepot.com/p/Gladiator-73-in-H-x-77-in-W-x-24-in-D-4-Shelf-Welded-Steel-Garage-Shelving-Unit-GARS774XEG/206727800
My sets are stored in the appropriate count BCW boxes and then in plastic tubs..
I'd also be concerned with storing cards "outside" due to temperature swings and humidity changes..I bought a lot of cards last year and some of the cards were stuck together, like bricks, not sure what happened but I'm thinking it was humidity..These were not your standard cardboard cards though..
Space quickly becomes an issue once the card bug has bit..I'd also ask you to think about if you ever plan on moving in the future because after I had bought close to a million cards (about a year ago), I got an out of state job offer and suddenly had a lot of cards to decide what to do quickly..I ended up selling a big chunk of them but still moved close to 150K cards for which my moving help (in laws) loved hefting around...
Bill