I want a practical advice.

A prof(PhD holder) from some college (different from mine) contacted me (19M degree adhi baki hai, har saal fail hota hu) to make drawings for his patent application (which got rejected). My patent was accepted successfully. He got my number through common contact. Thing is I will be required to invest my time and he didn't say a word about 'money', what should I do??? I want prize for my effort but saying no to him feels not good to me. Please help me out.