We wanted shelving in our wardrobe cabinet as well. I simply fastened small 1x1 pieces of wood to the backside of the wall that the wardrobe door was on. This supported the 1/8" plywood framed on the underside with 1x2. To support the back of the shelf (on an outside wall as well) I ran 1x2 strips of wood in a vertical position from the floor to the bottom of the lowest shelf and between each subsequent shelf thereafter . To hold these blocks in place I used sticky back velcro. I liked this method because they can be easily removed. A little over 2 years of use like this has worked out great.