When the company I work for had their shop in South Central Los Angeles, there was a tank manufacturing company next door. I don't know what part of the country you are modeling, but here in So Cal. many industries that would use a fully enclosed building elsewhere because of the weather, just use a roof with open sides here. A full size replica of that tank company would fit nicely in the space you have available. The tanks they made looked to me like compressed gas tanks, either for air or something like propane. Most stood vertical and were about 8' tall. The building was long and thin, just about two tracks wide with a small office off to one side in a "lean too" type sheet metal structure. The main part of the plant was an open shed made up of steel "I" beam supporting cross trusses that supported a sheet metal roof. There were two tracks coming in from the back with an overhead electric crane to unload mill gons loaded with flat steel stock. They cut up, shaped, and welded the steel into tanks. Scraps of steel were loaded into mill gons to go back to the steel mill. They would receive 2-3 mill gons of flat stock, and generally had two mill gons standing by to receive scrap. When the mill gons were full of scrap, the railroad would pull the loaded ones out and leave empties. I think they received the new steel about once a week. when the gons were empty they were pulled out, unless the scrap loads were full. If the scrap loads were full, they would move the empty gons that were just unloaded into the scrap spur, and take away the scrap loads. It would make a nice compact loads in/empties or other loads out industry. I think a combination of the Walthers shop with overhead crane, and Pike Stuff corrogated building kits could be used to make a believable building, and some tubing with dome ends and angle iron legs would make completed tanks. With a bright light in a workers hand, you could simulate someone welding up a tank.