All of the magi's sanctums/laboratories are wood enchanted with the Cabin of Earthen Wood spell, as is the Council Hall, the Common Lab, and the Revel Hall.
That was a miscalculation on my part. I've got the common lab statted up in the Covenant Description thread. It's actually size 1, about 675 square feet (half the length and half the width of the island, more or less centered on the island)