Builders have calculated the cost of Donald Trump’s Mexican border wall – in the hope they could help build it.

MH Construction bosses say they spent a week crunching the numbers before penning an open letter and tweeting President Donald Trump.

Martin Harnden, the Folkestone firm’s owner, said the idea began as a joke but “the conversation turned serious.”

“Someone’s got to build the wall over there.

“At first it was a bit of banter then it became a serious conversation because someone has got to build it over there.

“Also Donald Trump uses Twitter a lot, so you never know, he might pick up on it and like it.

“I know a lot of workers here who would go over and help build the wall.”

Mr Harnden believes it would take between 1,200-1,400 men six years men to build the wall.

In the letter, available on the firm’s website, it prices the cost of a 1,950 mile long 40 foot high pre-cast concrete panel wall at almost $22 billion.

An internal report by the Department of Homeland Security last year said the wall could cost about $21.6 billion, not including maintenance.

The letter continues: “50% deposit paid on account for the work is required so material etc can be ordered.

Please call to discuss an interim payment plan.

The balance will be due immediately upon completion.

It adds: “You should note that we have not performed a full inspection, we would obviously need to perform a site survey before any work commences.

“Call to discuss details.

“ If further issues are found, they will, of course, be discussed with you before any action is taken.”

The letter goes on to stress the amounts are estimates – and even calculates how many lego bricks it would take to build the wall.

Donald Trump today renewed a threat to declare a national emergency to fund the construction of the border wall.

A row with Democrats over funding has left the government partially shut down for 20 days, leaving some 800,000 federal employees unpaid.

On Saturday, the shutdown becomes the longest in history.

The White House has been contacted for comment.