How Ofter Should I Clean My Rats Cage?

I have two six week old baby male rats. They cage they are in now is small and only has one level. They use aspen bedding and nesting fluff. Would once a week be enough or more? Also I need a new cage what do you think of this one http://www.drsfostersmith.com/product/prod_display.cfm?pcatid=23204 and how ofter would i have to clean this one. would it change any since its alot bigger? Thanks in advance.