To add to what KE8NNP said… a ground independent antenna, such as the OmniX antenna does NOT mean you don’t need a proper ground for the antenna. They are two different things. You’ve still got to drive a ground rod into the ground or connect to an existing ground. You may have permission to put an antenna on the roof of the warehouse but the insurance carrier and the local fire marshal also have a say in your mounting the antenna. So, as long as you adhere to local ordnances and insurance requirements (they may differ) you should be all set in whatever you erect.
That OnniX sounds like a commercial antenna that may meet military specs. As such, anything built to those military specs are heavy duty and cost more, much more. There are cheaper options available that perform as well.