When I was a kid I didn’t have a Lego kit. I did have an Erector set but my favorite construction set was the “Girder and Panel Building Set” by Kenner. You used plastic girders to build a building and snapped on window or door panels. The way that the girders connected you could make a building with a cantilever section; that is an upper floor that juts out of the main floor. There were also blue plastic roof panels. Using the road sections you could make bridges or even roads that went through the second story of a building.
After making many buildings and tearing them down again the connectors on the ends of the gilders would break off making them unusable. The panels would also tear next to the hole where they would snap onto the girders. Still, I got many hours of constructing buildings and roads.
Another toy company has started making these sets again. You can tell the originals from the newer ones. The old sets have red girders and the newer ones have blue girders.