Changes diskspace size

Can you set up the subscriptions so it varies the size of the disk space allowed for a member?

Membership #1: includes 10megs of disk space
Membership #2: includes 50megs of disk space

And can the memberships be setup based on entering pass codes. Instead of using a credit card to purchase membership #2 they would enter a code for that membership and that would enable the new membership.

We are setting up a neighborhood community network and non of the memberships with cost $, they will be increased based on community involvement, so we would give out pass codes that would they could enter to activate the better valued membership. Hope this explains what we are trying to accomplish.