How to make Redmine create folders in redmine/files every new month with 775 for root:nobody?

Question

Redmine

Redmine runs on Ruby on Rails + Passenger + nginx.
Every next month a folder is created in /var/www/redmine/files/2018 with the month number.
The folder permissions are set to 755 for root : root .
Because of this, Redmine cannot attach a file, it pops up "internal server error" .
I change to 775 and the root group to nobody, the error disappears (permissions to write to the desired folder appear).
How to make Redmine create folders with root:nobody 775 every new month?