McDonalds used to have all their drive in areas done but most of them have their own pressure washers now, still worth a try though and KFC etc. Pubs, its hard enough getting them to have the carpets cleaned never mind outside. Have a look at some high end businesses like solicitors, accountants, marketing companies etc. Anywhere where clients visit the premises. These kind of companies like to make an impression so car park areas could be viable. Also petrol staion forecourts, canopies etc.