I'd say it depends what you want to achieve. To make it easier on the body, and make things practial, I might suggest that you do, on the 10 days you run: 18K, 0K, 18K, 0K, 18K, 0K, 18K, 0K 18K, 10K.
But if you're raising money for charity, and if you've got the time, it has a better ring to it if you do ten consecutive 10K runs. Probably a bit more risk of picking up a niggle though.
Whatever you do, I'm sure you know that you should build your weekly mileage up steadily, and concentrate on steady running rather than thinking about interval training or any nonsense like that!
Edited: 01/02/2013 at 12:27