Considering the lack of information as to the size, application, types of loadings, etc. it is hard to give any specific information; however, structural shapes such as I beams, angles, floor grating etc. for use in supporting structures, walkways and stairs for highly corrosive plant environments have been manufactured for several years by extrusion molding with a chopped fiberglass reinforced polymer. However, the finish of fiberglass molded components may not meet the level desired by your customer.
Also for a reference on a variety of molded polymer enclosures both large and small see the below website: