Position mirror in the center of the plywood sheet, and use construction-grade adhesive or wood glue to attach lattice pieces to the edges of the plywood, making sure the mirror fits snugly. Secure lattice pieces with spring clamps, and following manufacturer's instructions, allow the glue to set; this will probably take about 24 hours.
Line up molding pieces so that they extend just slightly beyond lip of the lattice, over the glass. Place a rosette block in each corner, lining up the ends of the molding with the rosettes. Glue the molding to the lattice pieces, taking care not to glue directly to the glass. Place towels over the molding to protect the wood, then weight the mirror with plywood. Allow to set about 24 hours.
Turn the molded mirror over to expose the back, and use the electric screwdriver to screw a 1-inch screw into the center of each rosette. Use two screws on each of the horizontal fluted molding pieces, spaced evenly, 1 inch from the edge of the wood. Use only one screw in each vertical molding piece, a third of the way from the bottom.
Attach the hanging wire using two D-rings: Measure a third of the way down the side of the frame, and attach a ring on each vertical molding piece, screwing them into place. Cut a length of picture wire long enough to run between the rings, with the peak of the wire 3 inches from the top of the frame. Twist an end of the wire into place on each ring. Attach a vinyl picture bumper on each corner on the back side of the frame; this will protect the wall from scratches.
Before painting, tape the mirror glass around the edges to avoid spilling any paint on it. Apply a coat of primer, allow to dry, and follow with a finish coat.
1/4-inch-thick mirror, 27 by 29 inches
1/4-inch-thick sheet of plywood, 29 by 31 inches
Construction-grade adhesive or wood glu
Four 2-inch-wide 1/4-inch-thick lattice pieces (two 27 inches long and two 31 inches long)
4 case moldings (two 25 1/3 inches long, and two 27 1/2 inches long)
4 rosette blocks, 3 1/2 inches square
Plywood, for weight
Electric screwdriver with Phillips head
2 D-rings, for hanging
Vinyl picture bumpers to protect wall
Tips: Visit a lumberyard or home-supply store to get unfinished molding, which is available in many styles, from chair-rail designs to the fluted case molding shown here. Paired with rosettes, the latter imitates a classic Greek architectural design. Most stock moldings only cost a few dollars per foot, but the finished frame will look anything but inexpensive. The following instructions will fit a mirror measuring 27 by 29 inches, but you can adjust the measurements as needed for your mirror.