Application Logic Design

Hi experts,
I need some suggestion helping me to have a good logic design.
My problem is this:
there is a web service (WCF) that exposes my business logic.
On the web service there is a method, for istance: public User CreateUser(User user);
When a consumer invokes this method I need to performe some step in order to create this user. For example:

1) create a new entry on the db (there is a data access layer that implements UnitOfWork and repository pattern);
2) Create some dns entry
3) Create a folder structure
and so on..

I need to make sure all these steps are successfully completed and in case of error I need to rollback.
My question is this:
What the best method (maybe using some design pattern) to help me to:

1) Send back the response to the caller only if all the steps are completed without errors;
2) Make the code flexible, testable and maintable (for example if a future step is needed I don't want to modify the web service bu just the business logic layer)
3) Is it better to pass back to the consumer an object that containes an error status ( zero if no error or some error code in case of error plus the response object like for istance responseObject.ErrorCode; responseObject.UserResult) or some object able to expose all the steps with their status (responseObject.DBSave = true, responseObject.DnsCreation = true and so on)?

Hope my question is clear and thanks in advance