if its a rich lich *hehe* ... then yep - he's gotta have a room for entertaining/reception/bragging - and several guest quarters, then there are his own rooms (one can't do it), and rooms for staff, kitchen, gardeners, guards, diggers, graverobbers, skeleton polishers and all that other needed personel ... maybe he acutally stole.. eh.. I mean, took over from the previous inhabitants as they left the ...life, thus their needs could set the standard.

if the star is a normal pentagram then you're stuck with that shape - but maybe it could just be a magic circle (not a star), that way it would take up less room ... if not, make the mansion star shaped - or at least use the points to house something