how to create master page for different user?

in the page Page_PreInit event, just check the user role and depending on that you can assign the corresponding master page. It should be something like

void Page_PreInit(Object sender, EventArgs e) 
{

        MembershipUser user = Membership.GetUser(Login1.UserName);
        if(Roles.IsUserInRole(user.UserName,"Administrator"))
        {
              this.MasterPageFile = "AdminMaster.master";
        }
        else
        {
              this.MasterPageFile = "ClientMaster.master";
        }
}

Note: Both master page files should have same structure and contentplaceholders.

Thanks.