You just want the SPECIAL EFFECT OF A CERTAIN AURA on building, yeah ?
Or you want the SPECIAL EFFECT + ITS EFFECT (+0.5% mana regen bla bla) ?
If you want the #2, you can edit a unit, using a BUILDING MODEL in Art - Model File and change it to ANY building-looking unit such as Town Hall etc
Change the Movement - Speed Base to 0 (well, building CANNOT move do they?)
Add the Brilliance Aura ability to the "building"
This can result in a Building-Unit unit
Well, this is what I've got