Sounds like he was in a manic psychotic state.
He probably had something pretty cool in mind when he went up there though

During the stand-off, the shaven headed man, who appeared to be in his 30s or 40s, had been yelling at onlookers and pacing up and down the billboard.
A man is undergoing a medical assessment at Royal Perth Hospital after climbing on to the top of a billboard near Perth's main train station yesterday afternoon, naked and armed with a gun.

I refuse to go into detail, but lets just say; freeing yourself from all material possessions can be quite liberating.