How to buy lots to build rental house

[Eben Cook]

What is the best method to basically cold call or write to a person who owns the vacant lot next to my rental house. I bought and older wood frame house with a lit attached where j built a 3/2 brick house that I also rent. Should I discuss willingness to further provide housing to people of the community. Any tips are greatly appreciated. I am new to this business. Just have the two properties but looking to increase. I don't know if building is better than buying. Thanks. Eben