Two construction workers perched on an I beam, assembling a building frame.
The men are working on something.
the construction workers are men
The construction workers can also be referred to more simply as 'men', the fact they are assembling a building frame indicates that they are working on something.
Men is a term for more than one male person, so two construction workers can be men. The construction workers are assmbling a building frame, so they are working on the building, or working on something.