Looking for an analogy for the Software Development process

What's the best way to explain it to laypersons not familiar at all with the process?

"It's like building a mode of transportation, but any component is available to use (wheels, jet engines, pedals), and some components are free, some are prebuilt for a price, and some need to be custom built…" or something along those lines.

Any ideas would be super appreciated. Thanks!