The 77-year-old was targeted at his home in Cardonald by two men who told him he needed repairs to his roof.
He handed over a four figure sum for the work.
But after looking inside his loft, the men then told him a further £4000 was needed to remove dampness.
The pensioner withdrew the sum from the bank but staff became suspicious and notified police.
Officers are now appealing for information to catch the conmen, who visited the pensioner first on Tuesday and then again on Wednesday.
Police say one of the suspects was aged between 30-35 and had stubble on his face.
The other suspect was around 50 and 6ft.
Detective Constable Raymond Hunter of Helen Street Police Office said: "Sadly, this is a typical type of crime that is carried out by cowardly individuals who have absolutely no respect for vulnerable members of our society.
"It is totally unacceptable to have elderly people feeling vulnerable in their own homes."
He added: "This man has lost a big chunk of his life savings and has been left deeply upset, and I would urge anyone who saw these two men hanging about, or thinks they know their identity to contact Police Scotland.
"There may be other people in the area who have been approached by these men, who haven't yet come forward to police.
"If you have had someone at your door recently that you were unsure of, or if an elderly relative has informed you of an incident, I would like to hear from you."
Anyone with information is asked to contact Police Scotland on 101.