An accessible or ADA/ANSI compliant style of portable restroom is provided. The portable restroom includes one or more of the features of: structural supports and/or curved sidewall segments allowing for the use of lighter weight material or construction of thinner walls and roof; improved holding tank structure; improved joints; vertical and horizontal grab bars; grab bar mounts which are molded into the restroom sidewall and facilitate mounting high impact yet flexible tubing; an improved lightweight floor structure, and a floor having upturned flanges which provide an area for attachment of the sidewalls; and integrated recesses in the floor for lift truck forks, among other features. A floor structure is also provided that comprises a sheet of material forming a floor, the material having an upturned flange surrounding its perimeter, and a threshold formed by a recess in the upturned flange on the perimeter of the plastic sheet. One or more self-leveling devices are provided for leveling the threshold and/or the floor.