Guys on the roof doing their work.
Workers are on the roof working.
Guys, who are workers are working on the roof.
exists e1 x1 x2 x3 x4.(n_work(x4) & of(x4,x2) & n_thing(x2) & n_roof(x2) & a_topic(x1) & on(x1,x2) & Theme(e1,x4) & Actor(e1,x3) & v_do(e1) & (x2 = x3) & n_guy(x1))
exists e1 p1 x1 x2.(n_roof(x2) & for(p1,e1) & Actor(e1,x1) & v_work(e1) & on(x1,x2) & n_worker(x1))