The federal government have released the requirements for the US-Mexico border wall design on Friday, describing the wall should be tall, climb-resistant, difficult to penetrate and blend into the landscape.

“The wall design shall be physically imposing in height,” Customs and Border Protection outlined in the notice for contractors. The government intends to accomplish a 30 feet tall wall, difficult to climb with ladders and gears although the officials wrote that “designs with heights of at least 18 feet may be acceptable.”

Moreover, the wall should resist attempts to penetrate through or under it. The request specifically mentions it must successfully endure for at least 30 minutes and ideally more than four hours. It also attempts to bore through it with a “sledgehammer, car jack, pick axe, chisel, battery operated impact tools, battery operated cutting tools, Oxy/acetylene torch or other similar hand-held tools.”

Aside from height requirements, the government also included “aesthetically pleasing in color” to US’ side, to its standards.

Interested bidders have two weeks to formulate a proposal complete with scale models to choose from. Various estimates have put the project at between $10 billion and $25 billion. Trump’s recent budget proposal requested $1 billion to begin the process.