The card base is 5" x 8". It is scored at 2", 4", and 6". It is then folded in half and cut from the fold line to the score line at 1 1/4", 2 1/2", and 3 3/4".
The 2 pieces of paper that are weaved in the slots are cut a 1 15/16 (1 tick mark less than 2") x 5"
This is how the card looks when you weave the pieces of paper in and it's completely open.
This is the card when it's closed (semi-closed in my picture). You can add an embellishment to help keep it closed.
Here is what the card looks like when you open the secret door.
Here is a link to the video I followed in order to make this card. http://www.youtube.com/watch/?v=KeSbbYawZDY