Cut two pieces of MDF, each 12 inches tall and 24 inches wide, using your circular saw. These are the front and back of your ottoman frame.
Cut two pieces of MDF with your saw, each 12 inches tall and 18 inches wide. These are the side pieces for your ottoman.
Measure and cut two 18-inch-long pieces of your 2-by-4-inch wood. Apply wood glue to the back of one two-by-four. Position it flush against the bottom of an ottoman side board. Secure the two-by-four by driving wood screws into the joints, using your drill. Repeat with the second two-by-four and side board.
Attach the front and back ottoman pieces in the same way. Apply wood glue to the edges and attach each piece to the edge of your side boards. Drill wood screws into the joints to hold the front piece and the back piece to the side boards.
Create a top for your ottoman by cutting a piece of MDF 18 inches tall and 24 inches wide; it should be the same size as the dimensions of your ottoman frame, so it can sit right on top. Secure the top in place with wood glue and wood screws.
Measure a piece of foam the size of your ottoman top, plus 1/8 inch to 1/4 inch on all sides; the foam can be as thick as you want. Cut the foam with a miter-box saw, an electric carving knife or a foam cutter.
Place a layer of cotton fabric over the foam so your ottoman feels a little softer.
Measure your ottoman from the bottom of the frame, over the top and down on the other side. Do this for the front, back, and sides so you have measurements for all sides. Add 1 1/2 inches to your measurement to allow for the seams you will create in your fabric.
Cut a single piece of leather so it matches your dimensions. When you finish, it should look like a large “plus” sign.
Fold your fabric together to make a cube and sew the seams together. Slide your leather over your ottoman frame. Pull it down as much as possible so it sits tight.