In my latest fortress, common rooms are 3x3 with a pillar in the center tile. I have four noble "palaces" laid out, each with a central 5x5 room ajoined by two 3x3 rooms, no pillars, all part of the same household. The four are actually laid out in such a way that they all open in the back to a central shared courtyard, about 8x7 with two pillars. Because my hallways are fairly stylized, with intersections opening into large circular halls before continuing into the standard one wide hallways in all directions, I have a fair amount of irregular dead space in my common housing areas, where a 3x3 won't fit. I recently put in "side units" that fill these areas nicely with common housing areas. As the irregular rooms have eight floor tiles each, they're each roughly equivalent to the normal 3x3 with a pillar rooms, so it works out nicely. I also have a few 1x3 "shacks" that just sort of got tossed in where there was space -- nobody uses those now, but if I need them, it'll be nice to be able to just throw a door on them. For any homeless, I currently just have a hostel next to the entrance to the fortress, which can be handy for when a wave of immigrants turns out to be about 50% bigger than was planned for.
I have one legendary stone crafter, and he spends all of his time making masterwork craft goods, instruments, and toys, all out of different colors of stone. Because his field of expertise is so narrow, and his assignment (crafts) is so large, I often see him squandering his talents on areas he has absolutely no ability at all in, like decorating bins with turtle shell, or carving bone arrows. I do have workshops assigned to do those things, because I think they're important, but what I really want to do is give him his own private workshop, where he can focus on the things he's actually good at, instead of gluing macaroni onto paper and trying to pass it off as his "legendary crafts" (he used to be a plump helmet planter, so he didn't even have pre-Artifact talent for decorating with turtle shells). For this reason, I think it would be nice if workshops could be "ownable" -- legendary dwarves really deserve the special attention anyway. I actually already have a special room cut out for him with room for a workshop, but I haven't yet installed one.