Should I build a NAS with the Raspberry Pi 4 or buy a Synology NAS?

[baydude]

Which one should I buy?

 

[hojnikb]

Depends on what you're after. With the new Pi, you have a lot of DIY options on what you can do.

 

[dave_the_nerd]

The Synology will perform better. The Pi will be more... work. But the end result may be better, depending on what else you do. (Case, PSUs, internal interfaces, custom programming, etc.)