One benefit of moving to Microsoft Azure is that you only pay for the resources that you use. To optimize costs, I frequently see customers trying to figure out what size data disks they should create when building a new Azure Virtual Machine.
Microsoft Azure makes this very simple. Always create the maximum size data disks, which is approximately 1TB. When using a Windows Server 2012 or higher virtual machine you will only ever pay for the storage used and not the total amount of storage allocated for the data disks.
Mark Russinovich provides a great technical overview on how this works in this video.