Determine the length and height of the stand-alone wall. You can place this wall along any section of a subfloor. Since it does not rely on adjacent walls for support, you do not need to line up the wall with an adjacent wall joist.
Cut two sections of 2-by-4-inch lumber to the length of the stand-alone wall with a circular saw to form the base and top plate. Cut additional sections of 2-by-4-inch lumber four inches shorter than the wall height to form the wall studs. You need one stud for each end of the wall, and one stud for each 16 inches of wall length between the end studs.
Lay the base and top plate on their 2-inch sides, parallel to each other. Place a stud at each end, perpendicular to the plates. Place additional studs perpendicular to the plates at 16-inch intervals between the end studs.
Check the corners of the frame with a carpenter's square to ensure that the corners form 90-degree angles. Drill pilot holes through the plates into the ends of each stud. Insert and tighten 4-inch wood screws through each pilot hole with an electric screwdriver.
Stand the frame on the subfloor in the desired location. Locate the floor joists beneath the subfloor with a stud finder and mark the joist locations on the bottom plate. Drill two 3/8-inch holes about two inches apart through the base plate into the subfloor at each mark.
Insert and tighten 4-inch-long, 3/8-inch diameter bolts through each hole with a ratchet.