Donald Trump can't just call the dude who builds his hotel when it comes to constructing a 2,000 mile-long wall, so we did some digging of our own to find out about the hoops that have to be jumped through.
Now that Trump has signed an Executive Order to build the wall, the Secretary of the Dept. of Homeland Security must do a comprehensive study of the Southern U.S. border to determine what fortification is lacking. There are areas that already have fencing and other barricades. The Army Corp of Engineers will most likely be tasked with doing a survey, which then goes to Homeland Security.
The survey must be completed within 180 days under the terms of the Executive Order.
At that point, Homeland Security then solicits bids from private companies to design and build the wall. The bids will be evaluated by U.S. Customs and Border Protection -- a division of Dept. of Homeland Security.
The Secretary of Homeland Security can't just write a check. He'll have to go to Congress for funding. It's estimated the wall would cost somewhere between $10 billion and $20 billion.
There is no time limit imposed on DHS to finish construction.