Is charge back by raw storage a good way to start?
If you have still most of your storage on DAS and you start, or plan to start, your storage consolidation program, I think you'll find it's simple to implement and requires only a little effort.
However, it should only be seen as a first step to get storage charge back running inside your company, as your pricing will still be unclear and your offer is not flexible enough to meet the different requirements storage customers have.
It's a good practice to start with storage charge back before you start planning storage consolidation. This way, you can prove that the storage department makes money, and it helps you to remember that every solution you evaluate has to be rechargeable.