A man sitting upon a roof is using a tool.
A huge person using a tool
There is a man, not just a person sitting on a roof using a tool and nothing indicates this man is huge
exists e1 e2 x1 x2 x3 x4.(Theme(e2,x4) & Actor(e2,x1) & v_use(e2) & n_tool(x4) & upon(e1,x3) & n_roof(x3) & Actor(e1,x2) & v_sit(e1) & (x1 = x2) & n_man(x1))
exists e1 s1 x1 x2 x3.(a_topic(x1) & Theme(e1,x3) & Actor(e1,x2) & v_use(e1) & n_tool(x3) & (x1 = x2) & n_person(x1) & a_huge(s1) & Theme(s1,x1))