Measure and mark 96 inches on all four boards.
Cut all four wooden boards at 96 inches with a table saw. Be careful when operating the table saw.
Cut the plywood into two 1-inch squares. Cut each 1-inch square diagonally in half.
Lay the four wooden boards in a rectangle. The side boards are on the outside of the top and bottom boards to make the screen 104 inches wide.
Place each plywood triangle in a corner.
Screw the plywood into the boards to fasten the boards together. This is the frame of the screen.
With the plywood joints on the bottom, stretch the white fabric across the wooden frame. You may want to have some friends help hold the fabric tight.
Staple the fabric into the frame on the back of the frame. Be sure there are no wrinkles in the fabric when you finish stapling. The fabric should be very tight.
Cut off the excess fabric.
All you have left to do is hang the screen up.