pls guys, someone wants me to help him to build a site like www.gumtree.com, but this would be my first project and i dont knw bout billing, he needs something of the same feature, but better graphics, so help me... What can the billing be like?
As mentioned, how much value do you place on your time? If you think your time is worth $10/hour, go for that. If you think your time is worth $50/hour, go for that. You can base it off of how much experience you have or how much your expenses are (or other things.. those are just two I thought I'd mention).
If you know how much other designers/developers in your area charge, you can base it around that number too.