I'm growing in a closet and used foil to create reflective walls around it. The final piece that goes over the door when it's closed is obviously a removable piece, which I made from a huge cardboard box haha!
It's working quite well!
You can technically make a little grow space out of almost anything, but consider air flow/humidity and how you'll get power to it! If you have any specific questions feel free to DM me, like about lighting or setup or how to craft a grow room ha. Good luck!