The Mercedes driver, who won the Chinese Grand Prix earlier this season, said that he was pleased with his day's work, having set the seventh fastest time of the day and finding a reasonable balance with the W03 in all conditions.
"I learned a lot because it was dry at some points this morning so we could do some dry running and I found an initial balance there, then very wet this afternoon, then quite dry with the intermediates so there was really everything," said Rosberg.
"So I have a good understanding and I am very ready for tomorrow and Sunday. Tomorrow looks like it is going to be wet and Sunday is looking like is going to be dry.
"I am going in a good direction and I am quite happy with the car initially. I like driving this track wet or dry it's always good."
Rosberg admitted that the penalty was a frustration for him.
"The only thing that makes it a lot more difficult is that I had a gearbox issue at Silverstone so we have had to change that and put a new gearbox in, and that means then that I get five places on the grid for Sunday - that doesn't make it any easier, especially since it is my home grand prix so that is not a nice thing."