Set the fence on the table saw 1/4 inch away from the blade and raise the blade to a height of 1/4 inch above the table. Run each 26-inch board across the blade so its 26-inch edge is against the fence throughout the cut. You will have a 1/8-by-1/4-by-26-inch groove on each board.
Set the 26-inch boards on edge, parallel, 25 inches apart, with the grooves 2 1/4 inches above the ground and facing each other. Set the 25-inch boards perpendicular between them so they are 25 inches apart and the corners are flush. Drill four countersink holes through each 26-inch board so two enter each end of the 25-inch boards. The 3/32-inch bit on the countersink should enter the 25-inch boards. The 3/8-inch hole should be 1/4-inch deep on the 26-inch boards. Screw the boards together using eight screws.
Turn your 26-by-26-inch frame over and lay your plywood on top of it so the edges are flush with the sides of the frame. Screw the plywood to the frame using 12 screws. Space the screws 8 1/2 inches apart.
Turn the frame over and slide your glass sheet in the grooves that were cut in the first step.