Stop in for a cup of coffee

That’s probably right. Most of that generation gas station had metal roofs. Almost all were oil company designs built to spec. The metal roof was designed to ensure longevity and offered a design distinction from other structures, highly visible in color to be easily identified by passing motorists. It was usually part of the entire visual appearance of the station so people knew exactly what it was. There were hundreds of service stations that looked exactly like my grandfathers station all over New England. The only design option was to flip the layout to have the service bay on the right instead of the left.
Makes sense. Clay tile has always been choosen to create a certain look. It's not something used on everyday buildings. Slate was pretty common in these parts, even on barns, but not clay. And blue glazed tile would have been special - therefore big bucks.