Usually for bedrooms I go with the up/down method
#=rock
-=space
i=up/down stair
j=down stair
u= up stair
z+1
########
- - - #- - -#
- j - #- j - #
- - - #- - -#
########
z+0
######
- i - - - i
######
z-1
same as z+1, but with up stairs
This can be repeated and works with a very small amount of room. I usually have a central staircase in my forts, so I put this near that, usually with a dining room nearby as well (on the z+0 floor). In my last fort, I also built a kitchen/fishery/butchery area beneath the dining hall and storage above, and three up down staircases with them. I use this simple design for dining rooms.
#=rock
c=chair
t=table
s=statue
##############
c c c c c c c c c c c c c
t t t t t t t t t t t t t t t
s s s s s s s s s s s s s
t t t t t t t t t t t t t t t
c c c c c c c c c c c c c
##############
The walls aren't important, I usually actually use a huge cavern to make this since it can fit huge numbers of dwarves in a small space. What I love about it is it takes all those statues you are mass-producing to keep stone levels down and actually makes them useful. In all honestly, if you put this design in an all rock area, engrave every tile, and use exactly this design, it doesn't take all that many rows to make a legendary dining room, probably 20 or so (never studied it in detail). This is nice if you like to have a few different living areas, and on top of that every time a dwarf goes in and out of their room, is going from the bottom of the fortress to the top or vice versa, or is actually eating they get the positive thought of going through a legendary dining room. There are so many statues that they often inspect them on top of that, and putting some food storage and kitchen areas above and below makes for very quick kill/gather to eat time.
As for offices, I don't have a definite design. Usually I do something like this.
#=wall
-=space
c=chair
t=table
b=bed
d=door
Manager/Bookkeeper:
- - - - - - - - - - - - - - - - - - -
#######d d##########
###- - - d - - d - - -######
###- b - d - - d - c -######
###- - - #### - t -######
###################
Kind of got messed up, but you get the point. As for my sheriff and leader who require nicer rooms, I usually just carve out 5x5 or so rooms with two space openings for doors for each of their needs, and engrave them. If I have a long central staircase, I'll often just carve them out around that, and leave the 4th side for expansion if I decide to expand.
I once tried to make a waterfall that caused mist to get into the mayor's office, but it resulted in a lot of unintended fun, so I don't recommend it.