Here is another Raspberry Pi robot that you can build to learn robotics and use indoors and outside. The MonsterBorg has an aluminum chassis, off-road wheels, and up to 3 hours of run-time. You can experiment with its code too.
The robot has 4x 300 RPM Zhengke 37mm motors, a ThunderBorg 5A motor controller, mount for the Pi camera, and 4 inch diameter off road wheels. Just bring your Pi 3, Pi 2, B+ or Pi Zero, batteries, and a micro SD card to get started.