How do I set up product dimensions for tiered pricing using SaaS Contracts (but not pay-as-you-go)?

Hello!

I would like to set up an AWS Marketplace offering using Contracts, but I am confused as to what a "dimension" actually is.

We would like to offer blocks of units with bulk discounts and hard enforcement of unit allotment, but without any pay-as-you-go.

Example: 1000 units/yr: $1000 5000 units/yr: $4000 10000 units/yr: $7500

etc.

What would my dimensions be in this case, and how would I enter them in when submitting my SaaS contract for review?