indeed, building vs using is an entirely valid hobby. some people like to repair cars for fun, or restore old ones. i knew someone who restored old steam engines. or people who like to restore/build computers from used parts and give them to kids who need one.

i built my own bike when i was young, but mainly because it was cheaper to get a quality bike that way and easier than saving up the money for a brand new bike. in the end riding is more interesting, so now that i can afford it, i just buy what i need.