Ask HN: How do you provide specifications/RFQ to a web designer?

I have spoken to a designer and he wants me to give him a high level spec, kinda like an RFQ. It is a web based application with the usual stuff like Users etc. I can write functional specs like I do at work but that seems too enterprise-y. Any other ways to do this specifically for a designer ? Should I just write Use cases with steps ? Should I draw some pictures by hand ? If someone can point me to some example specs, that will be great.