You will be billed for your first month of storage at the time you checkout (based on your estimated size). At MakeSpace you're only billed for what you store, so if you're put into a smaller plan than estimated, your initial payment will go toward your second bill. If you end up needing a larger plan, we'll just bill you for the difference.
Once your items are measured, you will be billed monthly according to when you started your plan.