If it is an existing, enterable building.... you can simply give the AI a waypoint that is placed directly on the name of the building... you'll know you've done it right if you can't move the waypoint after that....
now... when you edit the wapoint... you'll see there is a field for "position"
choosing one of the positions will make the guy go to that designated spot...
if there aren't positions.... you can always fool around with setposition
something like this:
this setpos [getpos this select 0, getpos this select 1,x]
where x is the height in meters above ground
:cheers: