I'm very satisfied with my DIY NAS. Of course, isn't perfect and isn't for everyone, but i enjoyed the build and i can be "proud" for my creation.
As you can see, SBC based NAS can work very well
But... from my angle of view, RPi isn't good choice for NAS build. Of course, you can build NAS with RPi, and it can works, but i thik, here are better boards for this purpose.
For example - NanoPI M4 - heart of my NAS have direct PCIe -> SATA (PCIe header & SATA HAT with Marwell chipset). With RPi, you must go PCie->USB (on baord controller)->USB to SATA(HAT, or USB to SATA cables). Plus problems with tons of cables, powering, etc...
Btw: SATA HAT for RPi4
I'm rather recommend NanoPi M4v2 with SATA HAT, or ODROID-HC4.
If your budger is low, you can buy only M4v2, SATA HAT, PSU (i'm running with noname 12V@5A wall plug - for now, my nas have enought power to run with two 3,5" Seagate IronWolf 4TB drives) and run in mess on desk. When you save some money, you can buy/make/3D print some kind of case.