In the order previously given, the flaps are successively marked, creased, cut to length, and folded over into closed position.

The lengths of the top and bottom flaps (the ones folded over and pointing up, in the image) are not critical; they just need to be long enough that together they cover the full length of the book, plus a bit of overlap.

The lengths of the left and right flaps need to be such that they are flush when folded over, i.e., 1W from their outermost creases.