I would click on the marquee tool and select the heavy line marquee (the light one affects the floor you're on and the heavy affects all floors). Draw that around the building and select all which will select the stuff on the floors above and below tho you can't see it. Now hit ctrl-e for rotate and select a corner of the building then draw the rotate angle down the building side, now the building should be rotating, rotate to approximately to where it should be then hit the shift key which locks the direction so you can get a definite 0degree lock then click. Before you hit escape to dismiss the marquee, you might have to hit ctrl-d to drag the building to be positioned correctly.
In the Options under Project Preferences there is a entry called Set Project North, use that to set north.
Also, look in the pic, there is a rotate orientation that rotates the x-y axis but only visually and that might help get the rotated building but keep the coordinates square.
Consult the help file for more info or if you need more help come and ask.
