craftgrrl | Jumbo knitted hat pattern

Hi all. I've just recently started teaching myself how to knit. My boyfriend asked me to knit him a hat for a valentine's day present. Problem is that with his dreads his head circumference is 28" (hence why he wants me to knit him one. He can never find any that fit!) I've tried googling for a hat pattern, problem is that most of them are about 22" and I don't know enough about knitting to make any changes to the pattern. Does anyone have a pattern that might be suitable, or tips on making a pattern bigger without adding too much length?

any help would be super