cone. >> reporter: professor deer is an expert in city and regional planning and the author of the book "why walls don't work." >> a large structure which might be 25 feet high which would be very intensive in terms of resources and money. >> cnn has hired a number of engineers and architects about what would be most feasible. the wall requiring, 339 million feet of concrete. the panels held together by 5 billion pounds of reinforced steel with an estimated cost of at least $10.5 billion and possibly much more. trump supporters say they can't wait to see the beginning of the border wall construction. >> that wall will get billionth and mexico is going to pay. i think he'll try to build a wall and i think he's trial to secure our boarders. >> if people want to come into