Well we are working with AWS for a start and planning to provide an equivalent behavior with Azure (as soon as it's available) and openstack.
The requested OS are Linux and Windows. Deployment is made from custom AMI. Post configuration will be automated using Chef.
Expanding the volume size is quite complicated on AWS (It require a snapshot / volume detach / volume attach / volume destroy). It would be easier to be able to specify the first volume size in the provisioning request/orchestration.
Unfortunately, it look like this is not handled in the current orchestration as instances are deployed with a volume configured with the default AWS volume size (8GB for Linux).
Thanks for your feedback.