Install Top Plates
How the top plates are installed depends on which direction the bottom plate is running in relation to the floor joists above. If the joists run perpendicular to the bottom plate then nail the top plates to the joists where they intersect. Where the bottom plate runs parallel to the floor joists, attach 2" x 4" blocking boards between the joists for something to nail into. Make sure the top plate is perfectly aligned with the bottom plate before nailing it to the joists or blocking. Repeat for remaining top plates.