How long does it take to build a full functioning robot?
What do you mean by "full functioning"? Like one that can talk and walk and run like a humanoid?
Robotics is already now very advanced and robots in automation and high order manufacturing are quite amazing what they are doing. If you look at how they build cars now with auto welding and parts assembly you would be amazed.
Recently a demonstration of a drivable automobile made from a 3D printing process took place; the final auto had only a few parts that were not made of a 3D printing system whereas present day automobiles have thousands of individual parts.
Panasonic claims to have a robot that can make lonely people feel like they have a companion around. It talks, sooths ones feeling, can sense sadness or happiness by listening to the sound of the owners voice. It can go to the kitchen and bring a refreshment, etc. Many plans are being made to build robots that will be valuable in several areas of medical delivery systems.
But, full functioning robots of the kind that you and I are most likely imagining may be many years away because we need to finish the work of learning how to think artificially. We don't have that yet.
Hope this helps.