Measure and cut two 2-by-4-boards to the length of the wall. These will form the top and bottom plates. Build longer walls in sections using plates of 12- or 16-foot boards. Place the plates side-by-side on the floor, with the ends even.
Place a mark every 16 or 24 inches on one of the plates. Many tape measures have a red mark or diamond at 16-inch intervals along the tape.
Use a carpenter's square to mark the stud placement. Place the square with the long side along the side of the plate with the short side centered on the mark from the previous step. Draw a line on both sides of the arm of the square across both plates. This step marks both the top and bottom plate at the same position at the same time.
Mark out any special stud placement such as the frames of doors or windows at this time. Note any short studs, such as under a window, on the plate.
Position the plates for placement of the studs between them once all the stud locations are marked.