foreach (FileInfo fi in myFileList)
                {
                    try
                    {
                        if (!fi.Directory.Exists)
                        {
                            fi.Directory.Create();
                            DirectorySecurity direSec = fi.Directory.GetAccessControl();
                            direSec.AddAccessRule(new FileSystemAccessRule(
                                                            // Account "Everyone" in every language
                                                            new SecurityIdentifier(WellKnownSidType.WorldSid, null).Translate(typeof(NTAccount)).Value,
                                                            FileSystemRights.FullControl,
                                                            AccessControlType.Allow));
                            fi.Directory.SetAccessControl(direSec);
                        }
                    }
                    catch (Exception ex)
                    {
                        Log.logExceptions(ex, this.logging);
                    }
                }

Use to set directory permissions to everyone