How to charge for shed cleanout?

I had an customer come to me today and ask if id be interested in cleaning out a large shed to he owns. He bought it from a antique dealer and this is apparently where he put all of his junk. He said there is some metal but alot of trash. I told him id come look at it one day this week when i get off work. I have no idea what to charge. Seems obviouse to tell him that i get all contents and he pays the fees from the dump. After that im not real sure. Charge by th hour? Flat rate? Any help would be appreciated. Thanks.