Coding user class best practice

I am implementing a custom user class, which is as follows:
public class User
{
public MembershipUser ...
public UserSecurity ...
public ParentUserId ...

public virtual void Save()
{ ... }

public User(string username)
{
// Load the membership user up
}

...
}I am then needing to extend the user class to varying types, e.g. Dealer. A dealer has set profile properties, and also has different create rules.What I'm wanting opinions on, is the best way to create a new user. At the moment, I have the following: public class Dealer : User
{
p ...