If you expect to use more than one container of paint, open them all and mix them together for a uniform color. You do not need to thin a paint for use on a floor One exception is if you use a sprayer that requires thinned paint.
Using a nylon brush, such as a 2½ sash brush, cut in the sides and corners with primer This creates a sharp, clean edge. Start this way for the top coat as well.
Using a roller pad with the nap length recommended by the manufacturer, apply a primer coat to the surface. Start at the corner farthest away from the door, and back up as you work. Allow the primer to dry for at least 8 hours.
With a clean roller pad, apply the first top coat. Make the top coat even but not too thick, then let it dry for 24 hours. if you choose to add another top coat, work the roller in another direction to cover any thin spots. Let the final coat dry another day before you walk on it.