Were I to do something like this, I would also use an Aura as a Magnitude guideline which I discussed here. Harry lives in dank basement under an old boarding house. I'd give his basement a +1 aura for the living quarters and a +2 for his lab. This gives him an overall +5 to +10 bonus when in his place of power. Places of power will be very valuable. In the Dresden universe, the owner or resident of a place has more power in their own abode. Might even bump up, like a specialty for an ability, so that whomever lives in the aura can better utilize it.
I just really like the idea of places of power, the idea that magi are secure in their towers, nigh unassailable, but that all changes when they go out into the real world. And then, if anything really bad does come to the tower, it's gotta be real bad.