The `build` method constructs the ORM object without validating or saving. It provides an opportunity to configure attributes before saving, before validating. If you feel good about the `params[:auction]`, have them filtered with `require` and `permit`, and aren't going to groom the record any further, then `create` or `create!` will serve. When using `create` it's necessary to check the return value for failures. With `create!` you'll have the `ActiveRecord::RecordInvalid` or other exception to capture on failure.