How long until we can build R2-D2 and C-3PO?

The Star Wars universe is full of droids. Everywhere you turn, there are medical droids, exploration droids, labour droids, pilot droids, even battle droids. They carry out clearly defined tasks, often with a degree of independence, without needing to interact with people. In real life, we now have the technology to create many of them ourselves. But what about robots that can also interact with people? When it comes to the likes of R2-D2, C-3PO and Force Awakens newbie BB-8, it's a much more mi