Along the same lines of itasha (otaku-decorated cars), itachari (bicycles), and other such fan-decorated items, the idea is basically a standard apartment building...but with a big fat piece of K-On! art on the side, as well as on the water tower on the roof. (Well, it wouldn't HAVE to be K-On!, but the particular model being sold at WonFes was.)
In fact, it was really just a clever repackaging of a building model with a bunch of K-On! decals, if you look at it really closely-- but I bet it sold like hotcakes. And it'll soon be available online for you guys who want to start building your own otaku city.
If it sells well, maybe before long you could have an entire K-On! branded replica of Akihabara or something. Would you WANT to own such a thing? And perhaps more interestingly: if you were going to live in an anime-branded apartment building, what anime would it be?
That's why Japan is so much cooler than living anywere else in the world.
What anime building I would like? Perhaps Code Geass or Ghost in the Shell: SAC.
Personally I can't think of any series that would make sense to have on the side of a building. I mean, maybe a few of those awesomely huge billboard poster things that Akihabara has all over the place on the sides of buildings, or maybe a giant grafitti style mech of some sort on the side, but official art kind of stuff? It just seems tacky.
I would like Maison Ikkoku art on the side of a apartment building.
*reads line* Waitaminute, that's not in the script. DIRECTOR!!!!