Construction of eight models in a remote area of San Diego is about three months behind schedule, held up by losing bidders whose protests were eventually denied.
A green tarp hanging on a chain-link fence blocked views of the work, which is expected to last 30 days and aims to halt illegal immigration.
The US Customs and Border Protection may pick several winners, or none. Roy Villarreal, acting chief of the Border Patrol's San Diego sector, said another contractor will evaluate each model, which will be up to 30 feet (9 meters) high and 30 feet long.
The construction site is about 2 miles (3 kilometers) east of San Diego's Otay Mesa border crossing at the end of steel-mesh fence that runs from the Pacific Ocean.