Do consult the local authority on whether you need an advertising license for your hoarding
 
Do think about working with a local artist or designer to create something original and eye-catching which will make your site into a local landmark
 
Do think about the kind of information you might want to convey - where will people be standing to read the information on the hoarding? It needs to make sense from near and far

Don't forget traffic and pedestrians who will be passing by - you may want to create an impression but you don't want to cause an accident