Designate one 12-inch-by-18-inch plank as "front" and another as "back" by marking one "F" and the other "B" with your pencil.
Create the front wall by clamping two 4-inch-by-4-inch wood-support posts to plank "F," making sure you align one post to F-plank's left edge and the other to F-plank's right edge.
Create the back wall by clamping two 4-inch-by-4-inch wood support posts to plank "B," making sure you align one post to B-plank's left edge and the other to B-plank's right edge.
Drill two bolt holes with the 1/4-inch bit in the front wall, vertically positioned (one on top of another), 1 inch apart, in each corner. Position the top hole 1 inch from the top of the board, and make sure to drill all the way through the support post.
Drill two bolt holes in the back wall, vertically positioned (one on top of another), 1 inch apart, in each corner. Position the top hole 1 inch from the top of the board, and make sure to drill all the way through the support post.
Secure the support posts by fitting a 1/4-inch bolt with a washer and threading it through the drill hole. Make sure to insert one bolt through each hole and cap it with another washer and a nut.
Finger tighten the nut and bolt. Tighten it all the way using the drill and the drill bit fitted with the 1/4-inch ratchet head attachment.
Create a rectangular box by clamping the remaining two 12-inch-by-18-inch planks of wood against the sides of the front wall and the back wall. These two planks will serve as your right and left side relative to the front and back walls.
Drill two holes, vertically 1 inch apart, in each corner of the right and left planks. Position the top hole 4 inches beneath the plank's top edge, so you don't accidentally hit the bolts drilled through the front and back walls.
Secure the support posts by fitting a 1/4-inch bolt with a washer and threading it through the drill hole. Make sure to insert one bolt through each hole and cap it with another washer and a nut.
Finger tighten the nut and bolt then tighten it all the way using the drill bit fitted with the 1/4-inch ratchet head attachment.
Form a cube by clamping a 12-inch-by-18-inch plank on the top of the box frame and the final 12-inch-by-18-inch plank on the bottom of the frame.
Screw a 2-inch wood screw into each corner of the top plank using the screwdriver. Position the wood screw 1 inch from the edge of each corner.
Flip the cube over so the bottom faces upward.
Drill a 1/4-inch hole in each corner of the bottom. Position each hole 1 inch from the edge of each corner.
Attach the wheels by threading a wheel bracket into each hole. Screw a wheel into each wheel bracket.
Place the cushion onto the top of the frame and cover it with the 44-inch-by-44-inch fabric.
Tuck the fabric beneath the pillow, creating a 1/2-inch "fold" beneath the pillow.
Staple the fold into place by lifting the pillow's edge and using the staple gun. Position each staple approximately 1 inch apart, and staple all the way around the pillow.
Apply a single thread of glue along the bottom edge of each wall using the glue gun. Make sure to lift the fabric so it won't get in the way.
Fasten the fabric to the sides of the ottoman by releasing the fabric and letting it fall down like a "blouse" around the bottom of the ottoman. Press your thumb against the fabric where you applied the glue, spreading the glue beneath the fabric. The glued fabric will then fit securely to the ottoman, and the remaining fabric that hangs down below the bottom will create a small "skirt" that hides the wheels.