Advice please on levelling a lawn

Hi, I am helping someone with their lawn as they would like to create a bed in part of the garden for vegetables and level the lawn.  There are dips of around 20cm deep and 4m2 in parts of the lawn, so substantially uneven.  I wondered if I could just hire a rotavator and rotavate the whole lawn (it´s not in a very good state) and then add top soil, section off the area for a vegetable plot, and reseed or turf the new lawn area?  

Any advice much appreciated!

Thanks.

Before rotavating remove any Cutch grass, creeping buttercups etc as you do not want loads of that regrowing. Otherwise what you have said sounds like how I would do it. I would go for turf as grass seed takes 1-2 years before it looks reasonable as you get lots of earth showing for a long time and there is not cushion of grass underfoot. You also cannot walk on seeded or turfed grass for a number of weeks so build the veg plot somewhere accessible.

Thank you for your help