Measure the sides of the wardrobe to determine how large you will need to make the shelves. Make sure you measure all four sides, even the open front, to make sure that the boards will fit inside.
Cut the wood slabs to the dimensions that you measured. You can stain or finish the shelves if you like. You can also trim a design on the front edge for aesthetic purposes.
Decide how far off the ground you want the first shelf to be. Measure up from the floor of the wardrobe and put a mark where the first shelf will go.
Make a continuous line around the three walls of the wardrobe starting from your mark. Use a level to make sure that you are drawing a straight line.
Measure up from the line a number of inches equal to the amount of space you want between the shelves. Remember that the shelf will take up an inch of that space. Make another continuous line around the wardrobe and do so for every shelf you want to add.
Make a vertical mark on the side walls a few inches in from the back wall on the bottom horizontal line. Make the same marks a few inches in from the front of the wardrobe. These marks are where your support pegs will go and need to be 2 to 3 inches in. Use the level to make additional marks on the other horizontal lines the same distance in from the front and back walls.
Drill ¼-inch diameter holes into the side walls of the wardrobe where you made the vertical marks. Drill between 1/4 and 1/2-inch in, depending on the size of the support pegs that you have.
Insert the support pegs into the holes and make sure the flat half of the peg is facing up.
Place the boards into the wardrobe at an angle and then rotate them straight and rest them on the support pegs.