Attach Drawer Fronts. You can do this after you have your drawers installed so that you can adjust for any slight discrepancies, but the location of the drawer fronts should be approximately what you see shown below in the diagram. There will be 1/8” spacing between the outside edge of the drawer front and the inside edge of the side panels on your box. There will also be 1/8” spacing above and below each drawer. There will be 1/8” spacing between the left and right drawers as well, but since they divide the space remaining, the overhang on the inside edges of your drawer fronts will be different than on the outside edges so I recommend using the outside edges as your guide.
The Fronts will sit flush with the drawer on the bottom edge, will overhang 1 ½” on the top and 3/8” on the outside edge. The drawer shown below in the diagram would be a drawer for left hand side of your unit if you are facing your unit. These measurements for the overhang will be on the other side for the right hand side drawers. Attach drawer fronts with 1 1/4” brad nails and glue, where the front meets the sides of your drawer box (otherwise the nails will stick out the back of the drawer face).