I was asked about making cards for friends, to give as gifts, so I decided to put this together, after working on some 'extra' cards left over from my class this saturday. I made the box, measuring the cards, to put all them together with the envelopes.
I made the template up, after seeing one close to it on Andrea Walford's blog, but smaller. But the dimensions are 7"x12". I scored 1/2" on either side (long side) and then 4 1/2", 5", 9 1/2", 10". You cut off the sides off the part where the 9 1/2" and the 10" score lines are (just the 1/2" sides) and that makes the flap. If you want a bigger box, to hold more cards, make the sides larger (increase the 7" size to 7 1/2") and score it at 3/4" so it makes the box bigger.