To do it legally, you'll have to get a permit for the billboard. Then you'll need to find someone who can install it -- so you know for a fact that it can be done. Are you aware that it costs about $4,000 to install the necessary hooks to attach a vinyl to a wall? Otherwise, you better come up with a plan to temporarily install it by attaching it to something else, like a balcony. But you'll not be able to do a large vinyl if you are just loosely attaching it (it will blow off). And then you'll have to put together a media kit and hit advertisers. And then you'll have to manage getting their design printed and installed.
Nobody said the outdoor business was easy.