Can you tell me how i could get buff without weights like in jail?

Absolutely: Read up on simple calisthenics and go at them with great intensity and variety. My favorite are "killers" -- stand, drop to pushup position, do a pushup or three, stand up. Keep it up until you can't, do many sets daily. Watch what you eat -- enough lean protein, fruits ; vegetables, and not that much else. What worked for young mr. Wahlberg behind bars will work for you.