Finally, I managed to assemble my first Arduino-based robot. I bought it from this Italian online shop. They provide all the instructions as well, but you also need some tools (screwdrivers, soldering tool, etc.) and some patience. It works fine! Thanks to a quite basic IR sensor, this small rover can avoid obstacles. Previously, I bought a ultrasound range detector: this one should be more accurate, but it takes more time to me to figure out how to fit it on the robot. More on this in a following post.
The next step will be to power it with a combination of solar panel and rechargeable battery pack. Stay tuned!