The proplem with trying to rake existing sod is you get large piles of grass and roots to get rid of. If the existing grass is good, I would get fill brought in and spread in the low areas with my bucket. Then try to rake the new fill just above the grass, maybe taking of 20% of the high spots down to minimize the grass collection, and chasing the new fill into the low spots to level the area and make it smoother.
The best way to get it flat is to of course tear it all right out, but that is a lot more work.
I leveled up a two 4 acres chunks of my old field area that was too rough to enjoy riding a atv on. The first I tilled , then began to rake thinking the several tandem truck loads of grass I was collecting, I could burn. But there was too much dirt in the grass for it to burn. I ended up piling it all up to let it rot down.
The second chunk I kept tilling to prevent the grass from growing for a whole summer and letting the old grass rot away. It raked up much nicer the next year with minimal debris to remove. If it would have been dryer I would have burnt it off first.
Also be sure to plan for where the rain water needs to go and creat some slope in the proper direction.