By coincidence, I've been thinking about almost the same issue for a bunch of aliens who aren't a human/horse chimera but share with centaurs the basic plan of quadruped locomotion and an upright "front torso" with two arms for manipulation.
I doubt centaurs would require their own beds or a room chiefly dedicated to housing a bed for a particular individual to sleep all night through. If centaurs sleep in a mode similar to horses they will do most of their sleeping in short naps taken a standing position, locking the "stay apparatus" in the muscles of their legs so that they can relax while still standing. However according to the Wikipedia link above, "Horses must lie down to reach REM sleep. They only have to lie down for an hour or two every few days to meet their minimum REM sleep requirements" - so centaur houses would probably be well supplied with bed/chairs available for any member of the household to use for a couple of hours at a time. I am visualising huge bean bags, but it is possible that they would actually prefer a pile of straw. Perhaps far from feeling that a stable-like environment is beneath their dignity they would consider the human habit of sleeping on artificial pads full of dust mites and shed skin cells to be unhygienic. Far better to have clean, natural straw replaced daily.
The ability to sleep standing up evolved in horses as a means to make a quicker escape from predators. For the same reason horses like to sleep in groups with one member of the group keeping awake and on guard. That's the basic evolutionary benefit of living in a herd. So at first glance it might appear that centaur households would need to be large, making for even bigger houses, and centaur lifestyle always communal. However centaurs are not horses. They can defend themselves extremely well, having both a man's ability to wield weapons and a horse's speed. This being so they could well be comfortable in groups of a wide spectrum of sizes, but probably never living alone. Much would depend on how "melded" the horse and human natures are in your centaurs, and how long they have been evolving for as centaurs. Possibly as mythical creatures they aren't subject to evolution at all, unlike my hexapod aliens.
Another thing that would differ a lot depending on the degree to which your centaurs were magical creatures with separate human and horse parts as opposed to evolved creatures that were more unified, would be kitchen and dining arrangements. For true dual-natured magical centaurs, C.S. Lewis's children's book The Silver Chair (one of the Chronicles of Narnia series) says it all:
“A Centaur has a man-stomach and a horse-stomach. And of course both
want breakfast. So first of all he has porridge and pavenders and
kidneys and bacon and omelette and cold ham and toast and marmalade and
coffee and beer. And after that he tends to the horse part of himself
by grazing for an hour or so and finishing up with a hot mash, some
oats, and a bag of sugar. That's why it's such a serious thing to ask
a Centaur to stay for the weekend. A very serious thing indeed.”
Now that I come to think about it, though, how would a centaur graze? His horse-stomach probably needs the grass, but it would have to pass through his human mouth and stomach first, which are not well adapted to either reaching, chewing or digesting grass. Returning to the subject of the question, any centaur home would require access to grassland, for psychological reasons even if not to provide nutrition. I do not think centaurs would be as willing as humans to spend all day indoors.
Centaur kitchens would be huge and continuously in use, resembling the kitchens of medieval castles.
In fact European castles of the Middle Ages and the sort of highly organised life that castle-dwelling fostered might be the pattern of domestic life closest to what centaurs would prefer. The fortifications would suit their horse-need to feel safe from predators, and given that every centaur is his own cavalry charger it might be needed to protect against enemies just as it was in human feudal societies.
Obviously the towers and upper stories would need wider staircases, especially if spiral, than human castles have - but horses can manage stairs surprisingly well. They don't find it easy to move backwards, so stairs and passageways would either need passing spaces and/or designated directions of travel as roads do.
If your centaurs follow the classical body pattern then to pick something up from ground level would require them to kneel down first. This is possible, but troublesome, so centaur houses would contain little other than floor and walls below waist level for a centaur which is about shoulder level for a human. All tables, handles, and shelves would start at this height. Delete the above if their "human" halves are adapted for grazing. In that case they might be able to manipulate things at ground level with their mouths as well as their hands.
The communal life within the castle, centred on the Great Hall with its huge dining table (no benches needed), would suit both their equine herd instinct and human sociability, with the option to retire to side-chambers on occasion for some privacy. (Note: sexual intercourse would not be included among the activities requiring a private room - it would take place outdoors.) Their human love of luxury and ostentatious display could be met as it was in castles by splendid wall-hangings and tapestries, rather than carpets or fancy, fragile furniture. Hooves are tough on carpets and furniture is going to have to be very strongly made to last long in proximity to horse bodies.
(Later edit: It has just occurred to me that though hooves are tough on carpets as I said above, hard floors would be equally tough on the unshod hoof. So unless your centaurs habitually fit horseshoes to each other, which of course they might well, they would like a softer floor surface than stone. So the top layer of a floor might be made of packed earth or sand by design.)
A description of the domestic sanitary arrangements necessary to dispose of the excreta of two differently functioning stomachs in one body I shall leave as an exercise to the reader.
