A platform trailer includes first and second aluminum beams. The first and second beams are defined with an arch. A platform is supported on the first and second beams. The platform includes a plurality of extruded aluminum panels that each extend from a left lateral end abutted with the left side rail to a right lateral end abutted with the right side rail. The extruded aluminum panels are abutted in series with the first end wall of one panel abutted with the second end wall of an adjacent abutted panel such that the respective upper walls of adjacent abutted panels of the platform together define an upper, cargo supporting surface of the platform. The platform is arched to correspond with the arch of the first and second beams. A method for constructing the platform trailer is also disclosed.