I want to modify an existing building and add a billboard to it. I have managed to alter the building and add an existing billboard. So that's done. However, I want my own personal billboard on it. I know what I want it to look like, but I don't know how to edit/make my own. I've watched a few tutorials on YT, but they either look confusing as heck (complicated) or just doesn't make sense. Any assistance would be greatly appreciated. Thanks so much in advance.

P.S. If you would like to have a go at it, I'm happy to forward my picture (?). Just lemme know. TIA