Other than having to maybe consider rotating the headstock of my lathe I've found that turning a large bowl or platter is pretty much the same as turning a smaller one.
The only real differences:
more weight so watch your back whilst getting the wood into place and don't drop it on your foot!,
consider using a faceplate with coach bolts rather than a chuck as you'll get a much better hold (particularly useful if your planning to core and save the middle),
use a slower speed,
take your time as there's a lot more wood to remove,
the lathe will take longer to stop due to the extra momentum.
If you don't have much experience doing small/medium work then I'd certainly recommend working up to the larger stuff gradually.