1 advantage of your own is the hdd wont be special PCB board connector rather sata so in future u can take out and plug in to pc internaly if needed when and if enclosure circuit goes bad hdd likely still ok.
The only drawback is not knowing if there's a HDD size limit for the sATA to USB 3.0 adapters (it usually has one). For example the box in the link posted by pisthai as a 32TB limit, probably 4x 8TB which is more than enough, but if the adapters from ebay have a 1TB limit it means I can never go over 4x 1TB. I'll probably go with the home built option simply because of the final cost, if I ever get to do it I'll post the results here