I want to write a young adults fiction book about a girl who buys an astronauts helmet from EBay and decides to see if she can then build a rocket to get to the moon. I'm a materials engineer, and with aircraft salvage yards and other resources I would think it is (just) within the realms of possibility if not probability, but obviously there are massive risk/barriers/etc. But, hypothetically, if you were to try it, what would you need. What would be the biggest hurdles, how you be creative to get around them.
Sadly not, the time is against you.
It took the labour of 200,000 people several years to accomplish the Apollo lunar landing. If you were to do that all by yourself, it would take you pretty close to 1 million years. Even if you could live for that long, the part of the rocket you started with would have rusted away long ago when you are finished.
As people have pointed out in the comments, the Apollo program was far from bare bones, and a lot of those person-years was used on research. But even if you could cut down the time 500x, the argument still holds.
It's not possible for a single person to make a moon mission.
The Apollo program is estimated to have taken somewhere around 15.5 billion man hours, even though some of the problems would be easier to solve now it would still take hundreds of millions of man hours (at least) to do it again. It takes engines providing millions of pounds of thrust, 7 million pounds of fuel and oxidizer, and vast amounts of specialized knowledge in hundreds of fields to make something like that work. None of that's on eBay.