Lay the two horizontal pieces parallel, spaced apart to match the rug's height. Place a 1x4 x 6' at the edge of one of the long frame pieces. Then on the other side, lay it on top of the other piece. Use a framing square and a measuring tape to ensure the vertical piece will fit perfectly in between the two horizontal pieces. Mark the exact length of the vertical piece with a pencil and cut it using a chop saw. Cut the remaining five pieces to the same length. At this point, you should have a rectangle frame with three middle support pieces.