In the core book, an important note (p221) on the extreme research saga:
Read several single-volume histories of
the area in question, to get a more balanced
view. Find, and read, histories of specific
aspects, such as the history of a single city, or
of the law, or of the Church, or even a single
monastery. Track down books written in or
about your area during the twelfth and thir-
teenth centuries, and read them in translation.
Learn Latin so that you can read the ones that
haven’t been translated yet. Learn paleography
so that you can read the ones still in manu-
script. Go back to university and get a Ph.D. in
medieval studies while actually just researching
... You may not want to get this detailed. But, talking to some colleagues down the hall in my department (of ancient history) led me to this answer. For an approximation, it's probably worth allocating a small house in the manor, say "servants live here" and only detail the precice floorplan if you must. On the other hand, if you feel like going on an archaeological dig, I do know who to ask for english excavations and what degrees you need.
But, to answer your question, ILL this book: Houses and Cottages of Britain
By R. W. Brunskill, and starting on page 114 for typical floor plans of houses. And then check out the multi-volume work: Greater Medieval Houses of England and Wales, by Anthony Emery. While it's a century too late, that certainly doesn't matter for this instance. Page 162 has important kitchen details, and suggests that the entire manor would share a single kitchen. Looking at the floor plan on page 161, the kitchen's size would be significant. Note that the "stanton harcourt manor" referenced is 14th century, and so has higher architectural development than would be the case for your magi.
When discussing this issue with my colleague, he mentioned that servants would have "not much space at all". Jugding from that and the description on page 159, the servants quarters (in their entire) would be one of the rooms near the kitchens next to the front hall. Apparently this closeness to the family was unusually high-status for the servants.
From my memory of prior research (without citation though) servants would generally sleep where they worked when the work-areas were not in use. Modern expectations of privacy would be an alien thing to them, and living conditions would be more about food quality, medical care, and a lack of beatings and angry men with pointy sticks than lebensraum.
For authentic locations and grey literature reports of archaeological sites in england, use the ADS. This reference (gained via ILL) will likely give you more details about farm servants which will provide for better extrapolation.
Compare to Covenants (p.103) the layout of the sanctum. This is the layout of the opulent-super rich magi in their well defended tower. They get a bedroom of about 25 square feet. Covenants does not otherwise go into too much detail about living quarters.
The answer you seek in context of the city townhouse is on page 22 of city and guild. The lack of dedicated servants' quarters suggests that my answer of "they sleep where they work" is appropriate. Use those buildings as templates for your skilled crafts people who may actually have a room to themselves, if they're particularly valuable.
Otherwise, to get a sense of relative proportion of floor space, look on page 63 of covenants and use relative proportion of living expenses modifier to provide for each individual persons' square footage.