Feed bin idea...Wall mount?

The accompanying photo shows a standard modern poly feed bin apparently attached to the wall of a steel building.  I'm curious as to whether or not others have seen such arrangements or built their own.  I'm even more interested in possible design variations where the tank is narrower, hugging more closely to the wall, yet still having the funnel effect at the bottom of the feeder.  We don't need to store more than 1.5 - 2 tons of feed at a time, so that size would do us fine.  I'd rather not have the bin outside like is often the case, and would rather use gravity feed to access the grain/feed instead of one of the electrical/flexible auger arrangements.  Thanks for suggestions and comments....