How are Samadhis/Chhatris are made?

I'm not talking about the spritual samadhi I'm talking about the tomb like structures of India kings. Like samadhi of Shivaji or Ranjit Singh what are the criteria of having a samadhi/Chhatris? What do you put there? Can children or women have them? Are they different? What are other ways the deacesed are remembered through a structures in Hinduism? Can we put flowers there as sign of respect and rememberence? How long is the tradition?