Measure your outdoor space with a tape measure to determine the desired length and width of the patio. Use the tape measure and a pencil to mark the length of the patio on two pieces of lumber.
Place a framing square over one of the marks and use the square's edge to draw a line through the mark and straight across the board's face; in lumber terminology, the term "face" refers to the 3-½-inch dimension of a 2-inch by 4-inch board, and the term "edge" refers to the 1-½-inch dimension of a 2-inch by 4-inch board. Lay out a similar line across the second board.
Cut the lumber to length with a circular saw, using the lines as a guide.
Subtract 1-½ inches from the patio's width to accommodate the thickness of the butt joint between the 2-inch by 4-inch boards. Mark the revised width on two 2-inch by 4-inch boards and lay out the cut line across the boards' faces.
Cut the boards to length with a circular saw.
Loosely lay out the cut lumber in the desired location of the patio. Stand one long board and one short board on edge.
At the intersection of the two boards, butt the end of the short board against the long board's interior face to form a corner. Drive two nails through the outside face of the long board and into the end of the short board.
Align the end of the short board with the adjacent, interior face of the long board at the opposite corner of the square. Fasten the boards with two nails.
Join the remaining corners; remember to keep the end of the short boards against the inside face of the long boards.
Drive stakes into the ground every 18 inches along the outside perimeter of the square frame, keeping the stakes flush with the outside of the 2-inch by 4-inch boards. If you are using wooden stakes, drive nails directly through the stakes and into the frame.
If you are using metal stakes, drive nails through the predrilled holes at the top of the metal stakes. Fill the interior of the square frame with concrete or install pavers.