Men with T-shirts on their heads

I've been watching these two workmen on the roof of the building across the parking lot from me. They both have T-shirts tied to their heads. Every once in a while, one of them looks down this pipe and the T-shirt blows up in the air. I have no idea what they're doing. One of my coworkers has some mini binoculars in his desk that he periofically uses to "spy" on people in the parking lot. I tried to use them to see what these men are doing, but I couldn't tell. Then one of them looked at my building and it seemed like he was looking right at me. Weird.