Cameron Diaz likes the "challenge" of recording 'Shrek'.

The 37-year-old actress - who voices ogress Fiona for the fourth and final in time 'Shrek Forever After' - confesses creating the character can be difficult for her because cast members are only given The Script on the day of recording.

She said: "It's a different kind of fun. The challenge for me is you don't get a whole script. You kind of get the script on the day and you're often reading it for the first time out loud as they are recording it. It's the first time it's coming out of my mouth. That's the challenge."

Cameron also revealed she liked Fiona's inner-strength, and is proud the green lovable monster has gone on to become a role model.

She told the Chicago Sun-Times newspaper: "Fiona is awesome because she is her own woman, her own ogress. It makes me feel so good to know that girls look up to Fiona as a role model.

"She stands right beside her partner and together they've created their destiny. She's also a rebel. No one is going to tell her to live a certain way."

Cameron - who has been nominated for four Golden Globe Awards - also admits she sometimes wonders why she takes on some of the film roles she does.

She said: "I look at the scripts as a whole. Sometimes that has gotten me in trouble. There have been times when I've done a film where I'm standing there in cold water or in a wedding dress or tied up. Then I realise, 'Why did you say yes?' But it's about looking at a script as a whole and you must do what's needed."

After finishing promotion on 'Shrek Forever After', Cameron will begin pushing her action comedy 'Knight and Day' with Tom Cruise, due for release in the UK on July 2.