As far as automating an out building, there’s a how to article in the community – created wiki which will lay out most of the options:
http://thingsthataresmart.wiki/index.php?title=How_to_Automate_an_Outbuilding
As far as ethernet – based home automation, I’ve been a network engineer for a while, and you just don’t see systems like this for several technical reasons. You create additional points of failure, you can easily run out of addresses, and the devices tend to have a higher power draw and to be more expensive. So it just doesn’t really fit the typical residential do it yourself low-cost home automation use case.
There are a couple of alternatives. The first is just to look into Insteon. It’s a perfectly decent home automation system with a lot of device options.
The second, specific to sensors, is to use hardwired sensors. These don’t have addressing issues, don’t add points of failure to the network, and are usually very cheap to run. You can combine these with SmartThings if you want, although you need to use an integration like Konnected
The third option is there is in fact a “Z wave over IP” protocol that was released about two years ago but the fact that almost no one is using it tells you it’s probably not going to fit most use cases. It does exist though, so I’ll mention it. But I will repeat again that even though it’s been out for two years no one is marketing it commercially. So I don’t think it’s going to be what you want.