I began with three cereal boxes. I taped them together with clear packing tape and cut the sides at an angle from the back down to the front, about 6" from the base. I didn't cut the front piece of the front box off at the 6" line, instead I scored it and folded it to the inside for added strength. I did the same for each joining of the boxes--I cut the back piece off to the height I wanted and scored and folded the front piece over the back piece and glued it to the inside. I used Tacky glue for this step. On the back piece, I folded the flap of the cereal box to the inside and glued it down for extra support across the back.
I cut the bottom overhang at an angle from the inside to the corner on the two sides and glued them down, keeping the fabric nice and smooth. Then I folded the other two sides in at an angle and glued them over the top. On the sides, I snipped the fabric straight in at the point where the boxes are joined, then cut each section at an angle to fit in place smoothly. The front and back were easy. I just cut from the outside edge to the corner, turned under the edges to make a slight angle and glued them down inside the box. I didn't cover the bottom of the box after turning in the ends, but if it bothers you, you can cover it with a piece of fabric or felt.
As a finishing touch, I cut pieces of fabric the width of the box plus 1", turned the side edges under about 1/2" and glued them over the two center dividers. The fabric doesn't need to go all the way to the bottom of the box inside, just far enough to keep the fiberboard hidden from view. Finally, I wrapped a piece of taffeta ribbon around the box, leaving the end at the front. I cut it into a V shape and glued a decorative button on the top. Instructions for making the decorative buttons are here http://snippetsnbits.blogspot.com/2011/07/handmade-decorative-brads.html. This one is done without the brad inside, but the process is the same, otherwise.
I now have a no (new) cost organizer for my desk to keep my loose papers organized that is also attractive. Win-win as far as I'm concerned.