As an active trader in this group 'Paper Traders'. I have hundreds of ATC size art pieces.
I thought this would be a fun way to store some of them.
Always make a template before you do your final cuts on good paper. I do this out of lightweight paper, so I can bend and mark till I get the size and shape I want. then I transfer all markings and fold lines to the final materials.
~Cut one sturdy background 14" x 3-1/4"
~Cut two pieces of pattern paper to 'wallpaper' both sides of the background.
~Mark your cardboard @ 2" then @4" then @8-3/4" then @10-3/4".
~Use a score board to score along your lines and fold so it makes a box with a bottom flap and a top flap. {I used a cereal box that had the exact size folds I needed for the top and bottom "2inches"}
~Use a score board to score along your lines and fold so it makes a box with a bottom flap and a top flap. {I used a cereal box that had the exact size folds I needed for the top and bottom "2inches"}
~Repeat the entire measure and folding with your decorative papers for inside and outside.
~Next wall paper inside and outside, make sure you secure it down really tight with glue. Clamp and let it dry overnight.
~Find the center of each end flap and mark about one inch down from edge to secure a button or toggle on each to close. The assembly took a bit of patience because I did it in two pieces so I could use the folds to their full potential. I glued clamped and let it dry. 
I used some scrap pieces that were about 2" wide and random length for the bottom.
{this is where you will secure your ATC pockets}
Each valley will hold a card holder, so do as many as you like. I have one that holds 12 and one that holds over 30. Your choice. Secure the accordion as pictured along the back spine.
Draw glue lines front to back along the floor of the holder.
Now make the pockets cut as many pieces as you desire at 6" x 4".
Score at 3-1/8" in from both ends. Fold to the center to form a pocket. Glue the bottom flaps and center back flaps at the same time. Cut a half circle out of the top center of each pocket so you can get your ATC's in and out easily.
Layer a quick grabbing glue in the valleys. Just do 4 or 5 at a time so your glue doesn't dry too fast.
I then went in and placed about an inch long piece of double sided tape just down from the centers and snugged each one to the one in front. This way when you open it, it fans nicely.
NOTE: I made three of these at once. I found I could just use the double sided tape and skip the accordion folded bottom step. Tape them all together first, making sure they line up perfectly. Make sure you secure the front and back pocket in securely if you do this. Have fun with this project.
