Tonido plug or similar device might be a good option? I'm considering getting one - mostly because (a) it's cool and (b) I have an at times irrational distrust of the cloud.
I investigated that option before building my own NAS, but decided against it. Plug computers offer no way to build RAID'ed systems, apart from maybe software raid over multiple external usb harddisks (I haven't tried it but I couldn't find anyone who did it, and I'm skeptical of performance of such a system). In the end I settled on a micro-atx board, a high performance power supply and lower energy use harddisks. I suspect (but have no data to prove it) that this uses less power than separate power supplies for each of the usb harddisks if one were to build a plug with those.
I'd concur. Especially since you can get actual barebones micro-atx servers for the cost of a nicer hard drive.