Measure the width and height of the space where you intend to place your open cabinet using a measuring tape. You will be building your cabinet out of 1-by-10-inch pine, so the depth of your cabinet will be 10 inches. For a deeper cabinet, substitute wider pine boards.
Cut two pieces of 1-by-10-inch pine to the desired width of your cabinet using a circular saw. These boards will be the top and bottom panels. Cut two pieces of 1-by-10-inch pine to the height of your cabinet, minus 2 inches, for the side panels.
Stand all four boards upright on their longest narrow edges. Sandwich the side panels between the ends of the top and bottom panels to form a rectangular frame. Drive 1 1/2-inch wood screws through the top and bottom panels into the thickness of the side panels to secure the frame.
Cut a piece of 1/2-inch plywood to the width and height dimensions of your open cabinet using the circular saw. This board will serve as the back panel for your cabinet.
Lay the back panel flat over one open face of your cabinet frame. Align the outside edges of the back panel with the edges of the frame. Drive nails from a nail gun down through the back panel into the pine frame to attach it.
Turn the open cabinet frame over so the remaining open side faces up. Measure and mark the position of your interior shelves along the side panels in pencil. You may choose to install your shelves at equal intervals or vary the heights to accommodate items of various sizes.
Use the circular saw to cut the shelves for your cabinet. Cut each shelf out of 1-by-10-inch pine using the width measurement of the cabinet, minus 2 inches to account for the thickness of the side panels.
Slide the shelves horizontally into place between the side panels where you made the pencil marks. Use a level to be sure the shelves sit flat. Drive nails from the nail gun through the side and back panels into the thickness of the shelves to install them securely.
Paint or stain your completed open cabinet to match the existing decor scheme in your room. Allow the paint or stain to dry completely before continuing.
Mount your open cabinet on the wall if you prefer a built-in look, or leave your cabinet free-standing. To install your cabinet on the wall, use a stud finder to locate the wall studs, and mark their positions on the wall in pencil. Hold the cabinet up with the back panel flush against the wall, and drive 1 1/2-inch wood screws through the back panel into the wall studs to secure it.