Due to the low cost and labour efficiencies of modern frame construction, the cheapest and easiest way to build a temporary garage wall is virtually the same as building any standard partition (non-load-bearing) wall, using 2-by-4 studs and 1/2-inch drywall. Save a little money and time by spacing the studs at 24 inches on centre (as opposed to the standard 16 inches), and it’s best to use screws everywhere instead of nails, so you can quickly remove the drywall and disassemble the framing with minimal damage to the materials and surrounding elements.
Mark the ends of the wall onto the ceiling. Make sure the top of the wall can be securely anchored to the ceiling joists or roof trusses, as applicable. Snap a chalk line between the marks (or draw a pencil line, using a level or a straight board as a straight edge) to create a straight layout line for the wall’s top plate.
Plumb down from the ceiling layout line, using a plumb bob or a level, and transfer the positions of the ends of the ceiling layout line to the floor. Complete the layout line on the floor, as before.
Cut a 2-by-4 top and bottom plate to equal the full length of the wall, using a circular saw or power mitre saw. Use standard lumber for the top plate, and use pressure-treated lumber for the bottom plate (moisture in concrete can rot non-treated lumber over time; use standard lumber for the bottom plate if the wall won’t be up for long).
Mark the stud layout onto the plates, using a pencil and speed square: mark for one stud at each end and one every 24 inches on centre in between. Position the top plate on its layout line and fasten it to the ceiling joists with 3-inch coarse-thread drywall screws.
Position the bottom plate on its line on the floor, and drill a few pilot holes through the plate and into the concrete slab, using a masonry bit and hammer drill (you can also use a standard drill, but it will take longer). Fasten the bottom plate to the slab with concrete screws.
Measure between each set of layout marks on the plates and cut a 2-by-4 (standard lumber) stud to fit. Install the studs between the plates with two or three 2 1/2-inch coarse-thread drywall screws driven at an angle at each end.
Measure and cut drywall panels to fit the full length of the wall or the framing layout, as applicable, using a straight edge and utility knife. If the wall is 48 inches or less in width and 96 1/2 inches or less in height, use one 4-by-8-foot sheet of drywall positioned vertically. Otherwise, run the panels horizontally.
Position the first drywall panel up against the ceiling and fasten it to the studs and top plate with 1 1/4-inch coarse-thread drywall screws. Cut and install the remaining drywall panels, leaving a 1/2-inch space between the bottom panel and the garage floor (to protect against moisture damage). If desired, drywall the other side of the wall.