"We will not go too far in our celebrations at winning the league because we want to win the double," said Rooney.
However, he admitted, after four years without the championship trophy, the Premiership was the number one priority.
"It was the target," he said.
"We have had 38 really tough games and to finish on top after that is great.
"There is no better feeling. It is what the hard work is all about.
"It is a massive thing to win and hopefully we won't have to wait another four years to do it again."
Fergie is pleased with the teams resilience:
"My players showed real courage and resilience to come through, especially when we were down to 14 players towards the end of the season. There is no question they will come on for what they have achieved this season."