To build a trellis, determine the dimensions that suit the space, and choose redwood, cedar or pressure treated-lumber materials. Select 5/8-by-1 1/2-inch wood pieces for framing, as well as 2-by-2 inch pieces for the body of the trellis.
Cut the upright grid pieces to fit the desired height of the trellis. Place the cuts face down on a flat surface, and put the correct spacing between each piece. Cut the crosspiece grid pieces the desired length of the trellis. Place the cut pieces on top of the upright pieces, and then use waterproof glue at each intersection. Secure the grid into place using nails or screws.
Cut the board for the top at the same length as the grid, and then the side pieces at the length of the grid plus the overlap of the top pieces. Add extra inches as needed to insert the trellis in soil. Use glue and deck screws to secure the side pieces into place. Place the grid so that it is against the inside of the top piece of the frame, as well as even with the back piece. Cut a piece of 2-by-2 so that it slides into place at the bottom of the trellis, and then glue and nail it into place.