The former Manchester United manager spoke at a memorial service for the former Rangers, Everton and Scotland manager.
Smith sadly passed away last month at the age of 73 following a three-year battle with cancer.
A number of people from the football world attended a service at the Glasgow Cathedral to pay their respects.
Ferguson recalled how he first noticed Smith's coaching talents during a course at Largs in 1972.
"Imagination, control of the session, he was a certainty to make it," the former Rangers player said.
Smith began his coaching career with Dundee United and Ferguson told how he failed to prise Smith away from Jim McLean. But he later briefly employed Smith as his assistant with Scotland and Manchester United.
Ferguson told how Smith refereed training games and would take a lax approach to challenges on Ronaldo, who 'came with all the tricks in the world and wanted to beat all the players'.
"He walked up to me and says 'Boss, do they not have fouls in Scotland?' And he learned. He learned how to pass the ball and he can thank Walter for that. No question."
Summing up, Ferguson borrowed a phrase used earlier by Smith's younger brother, Ian.
"I was looking for a word that encapsulates this man and it's definitely giant," he said.