I have three NASs (2 x 8TB and 1 x 14TB). I can access my 14TB via Netgear's Ready Cloud. However, that NAS stores primarily photos and music/videos which I don't access on a daily basis. Everything else is on OneDrive. ALL of my devices are connected via OneDrive and those files I can access much quicker.
The problem with personal cloud storage is that you still don't really have an offsite or separate back up. The other problem isn't so much as costs. You can build a 14 or 16 (or more) TB NAS for just under $500 (depending on the drives you choose). The problem is that personal cloud storage requires a certain amount of not only networking knowledge, but a fairly good understanding of security and protocols as well. When you purchase cloud storage from Microsoft, Google, Amazon, or any other provider, you are not just purchasing storage space, you are also purchasing security and maintenance. There are people in Microsoft who are a LOT smarter than I am when it comes to security and protocols.
Fun fact: Microsoft experimented with unlimited OneDrive space. If you were a Office 365 subscriber (which I am), you could request unlimited storage. Microsoft would give you 10TB of storage, if you used that up, you could request another 10TB. The problem was people immediately used it as storage for ALL of their videos. Some people were using a much as 50 or more TB of storage and then streaming those videos, which sucked up bandwidth and server cycles. After about a year, Microsoft discontinued the unlimited offer.