Note: Quantities of the materials will vary from job to job.
Examine the area where the bench will be built, take all the necessary measurements and notes. Use a chalk line to mark out the area where the bench will sit. Clean and prep the area.
Cut the 2x4s to length for the bench frame. If necessary, adjust the length of the upright pieces to accommodate any uneven spots in the floor. Use a hammer drill to attach the back and side sections of the frame to the walls. Then attach the upright pieces to the walls so that the bottoms sit on the floor and the tops butt up to the back and side sections.
Build the front section by nailing 2x4s to form the front and sides. Line it up with the marks made earlier. Attach the L-shaped frame to the back and side with wood screws. Both ends of the L frame should make contact with the corresponding walls. Make sure it is level with the back section. Attach the ends of the L to the back and side sections with screws. Repeat for the bottom of the front section, but use the hammer drill to attach the lower section to the floor (use 3" concrete screws for concrete floors). Measure and cut pieces of 2x4 to fit between the upper and lower Ls on the front and side. Position the upright pieces between the top and bottom plates of this front section and directly across from the upright pieces on the back. Hammer them into place and secure with screws.
Attach another 2x4 to the front of the back support along the wall, effectively doubling it up. Screw a 2x4 flat against the bottoms of the upright pieces against the wall on the back and right side.
Measure the inside of the bottom of the box. Cut pieces of 2x4 to fit on the floor between the front and back bottom plates where the upright pieces meet. Keep these 2x4 supports lined up and level with the top of the 2x4s that were attached to the wall. Predrill the bottom supports so they can be toenailed into the bottom plates. This is where the 3/4" plywood bottom will sit.
Cut and attach 3/4" plywood to the outside of the frame. Keep the top edge of the plywood flush with the top of the frame. Cut and attach the plywood bottom to the inside of the frame.
For the top, cut a piece of plywood 1 inch longer and wider than the plywood-covered frame. Draw a line down the length of this top piece 3-1/4 inches in from the edge. Using a circular saw, rip down this line to separate the top piece.
Attach the 3-1/4" top plywood piece to the top of the doubled-up 2x4 back support, using an 18-gauge finish nailer. This is the section of the top to which the strap hinges will be attached.
Cut the top plywood piece 1 inch longer the length and width of the plywood covered frame. Draw a line down the length of this top piece 3-1/4" from the edge. Using a circular saw, rip down this line to separate the top piece.
Attach the 3-1/4" top plywood piece to the top of the doubled up 2x4 back support, using the 18-gauge finish nailer. This is the section of the top to which the strap hinges will be attached.
Line up the larger section of the top with the smaller section that was just attached. Separate the two top pieces where they meet, using 3" framing nails as spacers. Determine how many strap hinges to use, then mark their locations. Use one strap hinge every 16 to 20 inches.
Attach the stationary part of each hinge to the 3-1/4" section of the top with 1-1/2" wood screws. Make sure these screws sink into the supporting 2x4s. Attach the strap part of the hinges to the flip top. Paint or stain the outside of the bench.
Cut the 1x4 clear pine pieces to length, and attach them along the top and bottom of the visible face of the bench to create horizontal trim.
Cut some 1x4 pieces (stiles) to fit between the top and bottom trim. Start by covering the plywood corner and work outward. This style of trim will create a panel look. The number and spacing of the stiles used is a matter of personal preference.