Um... like a giant birdhouse? Okay, so it would have this entry door hole thingy, and so they get in by tapping the door in a certain sequence because otherwise the dinosaurs could get in. One big open room. Floating in the sky.

Yeah. I really have no idea.

Ooh! This'll be really fun to think about! I'll do it one step at a time.

Well, if birds had 15-foot wingspans, they'd have to build enormous places, but they'd also have to find room. Trees wouldn't work; there are no extensive prairies anymore; I can only think of a few options. For one thing, they could build them on the tundra, but it'd have to be in one of those places so far from the equator that the ice didn't melt even in the summer, if it was a permanent residence. If there were many of these birds, this wouldn't work, but if they had human intelligence, they could find a solution. They would need it to move, though, since they'd be extreme cold-weather creatures. They'd have to invent air-conditioning and build habitats not unlike those that zoo-keepers make for penguiuns--but much, much larger and also better furnished (We'll get to the inside of the place later), and of course, if you don't want these birds to be good swimmers, there would be much less water. They'd need access to a food source as well.

Another possibility is one I'm basing on the wandering albatross, the living bird with the largest wingspan. This possibility is that they don't have houses or nests or anything of the sort for most of the year because they spend most of their lives on the move. The wandering albatross can travel 6000 kilometers in 12 days and only lands to breed and feed. This bird can have a winspan of up to 11 feet, but the nest is only one meter wide at the base and half a meter wide at the apex because they don't spend much time there; it's just a place to hold the egg. It's basically a big bowl of grass, mud, soil, and peat I'm guessing that if the wandering albatross had human intelligence, it probably wouldn't change too much other than getting a better security system and maybe inventing a way to incubate the eggs without having to sit on them themselves.

Alternatively, they could build their shelter on a prairie or savannah. There would be plenty of room here, and although they'd be rather exposed,  I'm sure they could think of a way to avoid predators. This might be the closest thing to a house we could expect, since conditions would be similar to those in which humans first started building houses. They might be built of a mixture of soil, grass, mud, saliva, and other soft, sticky things. Perhaps they'd think of bricks; perhaps not. Would they have roofs? I think they might be a good idea.  These shelters might be dome-shaped.

Another option is using trees as beams and putting a roof over them. They could keep mostly hidden this way, and it wouldn't be difficult.

That's about all I can think of, unless they lived in the desert and made pueblos or burrows or something. Now, furniture. I imagine they'd have fairly highly developed security, as mentioned before, so as to not let in egg predators. This might mean only one parent would need to care for the egg, which often happens with real birds, anyway. I'm sure they'd have a good heating system for incubation, as mentioned; beds, couches, chairs, etc could be nestlike, and tables wouldn't really be necessary. I think the sorts of tools they use might be very different from ours because they'd need different things. Of course, if you used the albatross-based idea, they'd have very little furniture, possibly none besides some tools and definitely some heating and cameras and alarm systems and so on. I think some aesthetic quirks might be interesting--birds have different taste than us. You can look up bowerbirds if you want; they decorate more than most birds, and it seems really bizarre to us, and I imagine intelligent birds still wouldn't fit human norms on the subject, so decorations could be really interesting--colorful, definitely... That's about all I can think of at the moment, but it was fun.

I don't really think they would be stereotypical. Since it's human intelligence, they would use their superior bodies to take control of humanity and live in our homes with us as pets. 

I'm going to answer this the Melody way (a.k.a. using randomness as my guide) and say in giant doughnuts.

Hmmm.... Well, you could make them live in giant human houses. Or maybe, big houses with one giant room with a nest in it. I dunno. I'll try and bring it up with my family at dinner.