Construct the frame for the bleachers using 2-by-4s. Start from the bottom with a large rectangle which will be the footprint or base of the bleachers. Be sure that the base is stable with many supports. Using a support every 18 inches will ensure that the bleachers will be sturdy.
Install 2-by-4s perpendicular to the base of the frame. These risers will be what supports the 2-by-10 benches. Measure the first set of risers to be 18 inches from the base. This will be the first bench. Measure the second set of risers to be only 12 inches from the base. This set of risers will hold 2-by-10-foot rest for the second benches. The third set of risers should be 24 inches from the base. This set of risers holds the second bench. By staggering the risers, it is easy to create foot rests for each successive bench. Again be sure to use ample supports to hold the weight of many baseball fans.
Add more risers until you reach your desired number of benches. Plan ahead so you have enough room on your base for the target number of benches. Stagger each bench and footrest 18 inches behind the other.
Screw the 2-by-10 benches and footrests onto the bleachers. The length of the 2-by-10s can be 12 inches longer than the total length of the frame. This will allow the bleachers to jut out slightly from the frame. Use plenty of long deck screws that will anchor the benches well.
Sand and finish the bleachers. Use a coarse grit sand paper and slowly work down to a fine grit to make the bleachers smooth. To complete the authentic feel, give the bleachers several coats of finish and wax. Sanding and finishing will prolong the life of the bleachers and cut down on any potential splinters.