FileManagerRootFolder root = new FileManagerRootFolder();
root.Name = "<name>";

root.Location = 
    "Path={<physical path>}; " +
    "User Name={<username>}; " +
    "Password={<password>}";

FileManagerAccessControl access = new FileManagerAccessControl();

access.Path = "\\";
access.Quota = new GleamTech.FileUltimate.AspNet.UI.ByteSizeValue(62914560); // 60MB
access.AllowedPermissions = FileManagerPermissions.Full;

root.AccessControls.Add(access);

fileManager.RootFolders.Add(root);