Freshly milled oak is quite heavy and can be difficult to work with. However, using green wood can lead to some unique pieces. It's essential to consider the shrinkage and movement of the wood as it dries, as it can cause cracking and warping if not appropriately handled. Do some test pieces first to see how the wood behaves.
If you're looking for more inspiration or ideas on outdoor furniture, you can always check out different websites or local furniture stores and click here. It's also worth considering different types of wood and finishes suitable for outdoor use. As for your client, it's best to be transparent about the potential challenges of working with green wood and let them decide if they're still interested in going forward. Good luck with your project!