Measure your cellar windows. Write down the dimensions, including the height, width and depth.
Put on safety glasses. Measure and cut a piece of 1-inch by 1-inch pressure-treated lumber with a miter saw to the dimensions fitting your window. For instance, if the cellar windows measure 36-inches wide by 30-inches, cut two pieces 36-inches in length and two pieces 30-inches in length. Use the angling on a miter saw to cut 45 degree angles on each end of each piece.
Connect the four pieces of cut 1-inch by 1-inch lumber with wood glue, then staple together at the joints with staples to make secure. Allow the glue to dry for 4 hours or as long as recommended by the manufacturer.
Stretch window screen over the frame and cut around the outside of the frame, leaving about two inches of excess.
Situate the cut screen over the frame and staple into place, stretching the screen as it is stapled to make it taut. Once all four sides are stapled, cut the excess with a utility knife.
Insert your custom-made screen into your cellar window and proceed to make others as necessary.