They've put together a detailed list of 70 buildings, along with what exactly all of them do, and what size plot they go on. There's a lot of interesting information one can glean from this data, such as how follower gearing might work and what mission rewards might be, as well as how you get various vendors into your Garrison. Of course, this is datamining, so shouldn't be taken as 100% fact, but it's still really interesting stuff.
There's also information showing off small images of the Garrison buildings, and a map. It seems like these may be UI elements that allow you to design your Garrison and set up its layout, but of course, this is just inference from the data that's presented. There is, however, even more information on each building type, that ties in with the aforementioned list. We're slowly getting an idea of what the Garrison progression might look like.