So you would like to build fun robots with Raspberry Pi 3 B? This AlphaBot2 Robot Building Kit has you covered. It can be used to build a robot for line tracking and avoiding obstacles. You get Bluetooth/IR/WiFi control and video monitoring.
The robot has a modular design. It comes with a 40-pin GPIO, camera, and display interface. It is powered by a 1.2GHz 64-bit quad-core ARM Cortex-A53.