What are the opportunity costs of building a wall on the southern border of the United States?

SOURCE: Fox News

The economic principle I will explore is : Because of scarcity, people choose. All choices have an opportunity cost. Economists emphasize that we live in a world of scarcity. By this, they mean that there are never enough resources to provide all the goods and services that people want. The result is that people must constantly choose among competing alternatives. 

The overall question I will research to help explore the economic principle is: What are the opportunity costs of building a wall on the southern border of the United States?

 3-4 sub-questions that will help me answer my overall research question are:
1. Would it help or harm employment? How much would it cost to build? 
2. Would it affect the rate of illegal immigration? 
3. Would the state of the economy improve? 

Links to 3-4 reliable resources that can help answer the research question:
1. Am Greatness 
 2. Market Place
3. Heritage
4. Market watch