Starting a digital billboard advertising company from scratch?

In the interest of keeping my post short, I'm researching how the digital signage & advertising business works. I'd like to get into the business, starting from the ground floor, whether that be investing in my first digital billboard (computer-controlled electronic display for out-of-home advertising), or buying into an existing sign that already exists on a building somewhere. Anyone have experience in this field that could let me know how to get in on the ground floor?

Below is an image of my long-term holy grail, owning a digital advertising screen in one of the busiest pedestrian intersections in the planet (e.g., Shibuya 109, Tokyo, Japan)
Shibuya 109 in Tokyo, Japan