I like doors on my cabinets to keep the dust away, so I totally dig what Massimo did to his low single Billy.
“My goal was to realize a little cabinet nearby the entrance of my living room. I just bought a Billy frame and two little doors made for the height extension unit. The problem is the frame holes don’t match with the doors mechanism. After measuring the best placement of shelves and doors all together, I drilled eight new holes with a 5 mm drill bit to fix the pivots. The result is a brand new cabinet (width: 40 cm, depth: 28 cm, height: 106 cm) with an open shelf completed by a little wicker basket (perfect to empty my pockets) and two nice compartments to change the bookshelf look of Billy system.”