The first step was a complete disassembly. That put him here.
This isn't the start of a restoration. It's a 3D model of a wooden wheelbarrow. There's just enough remaining to use as a guide to fashion replacements. He uses a few salvageable parts from the right side in the finished product mostly as an homage.
It's a great job and a good video, even if you skip along, worth it to see the finished project.
There are a few things that make this project possible. He had the wreckage of the original. He had the skill, the tools, and the interest to take on the work. The scale of the project was manageable. That last one, given the state of decay, is crucial. He might have been able to save a horse drawn wagon in a similar condition. But a barn? A church? A boat?