I think rough hands could symbolize how hard we work in life, and maybe its meant to be a bit of irony, because Oscar doesn't think life has a point. So in his mind, in may be seen as : we work really hard, but for what reason?
This isn't really about rough hands, but it is a good hands metaphor that I liked. "She was extending a hand that I didn't know how to take, so I broke its fingers with my silence." (30)
"Oh. And what about his hands were so rough and red from all of his sculptures that sometimes I joked to him that it was really the sculptures that were sculpting his hands? Over." (71-72)
An example of rough hands is the sculptors hands. "I assumed his hands were so rough from all of the sculpture he used to make." (83) Rough hands could also symbolize hard work and suffering. The sculptor would have had to been sculpting for many years to develop the rough hands.
--Oskar's Grandfather is the sculptor with rough hands. We find this out later in the book through the "WHY I'M NOT WHERE YOU ARE 9/11/03" chapter.
"She tells me the same stories about Grandpa again and again, like how his hands were rough from making so many sculptures" (104)
"From behind a column I watched him write more, and ask for the time, and rub his rough hands against his knees." (179)
"The silence pressed down on us like a hand." (210)
I know it's not rough hands, but the hand is symbolizing a greater force, similar to rough hands.