Clean the rafters or crossbeams of the roof area with a broom. Knock lose any dirt, tree needles and spider webs. If the roof is covered with wood or tin, remove this before beginning the screen installation. Work inside the structure when installing the screen roof.
Measure the area between the roof beams with a tape measure. Cut a piece of screen mesh with scissors 4 inches wider and longer than the measurements. Cut two thin wood slats the length of the measurement and two more for the width with a saw.
Spread the screen mesh across the opening, leaving 2 inches of overlap on all sides. Place one staple through the screen in each corner of the opening with a staple gun. Pry out any staples with a flat-bladed screwdriver if the screen needs readjustment.
Staple the edges of the screen to the crossbeams, while stretching the screen mesh tightly. Place the wooden slats over the staples and nail them in place with finishing nails. Trim any slat that does not fit properly, with the saw. The slats help hold the screen firmly in place.
Trim the excess screen away by cutting the screen just under the wooden slats with a sharp craft knife.