Draw straight lines on the acrylic sheet with a thin-tip permanent marker so you will know where to cut. You will need to measure and mark five pieces: the top, two rectangles the length of the art and two the width of the art. These will be the sides of your box. They should be high enough for your raised art to fit underneath.
Score the acrylic just inside the marker lines with a razor blade or sharp craft knife. Flip the acrylic over and score the other side of the sheet along the same line. Bend the acrylic back and forth along the line until the pieces break apart.
Lightly sand the edges with medium-coarse sandpaper.
Put the large acrylic piece flat on a table or countertop. Select one of the sides, and hold it at a 90-degree angle in its desired position against the top.
Apply the acrylic cement into the joint. Allow to set for at least 20 minutes while holding the acrylic at a 90-degree angle.
Repeat the cementing process for the other three sides, and the side joints. Allow to dry for at least 24 hours before placing over your artwork.