You can look up object IDs for the buildings using the editor. Then give the unit a TALK waypoint, and put this code in it:
this domove ((position this nearestobject 259904) buildingpos 10);
The unit should then move to the position in the building (including second floor positions). Note there a re a few buildings where AI get stuck (like the tall apartment buildings in Bagango). The AI cannot access the upper floors of those buildings for some reason. Also note that when using code, the building positions are start with zero, but when you are playing and ordering units into buildings (so the building position # is shown to you while playing) the position #s start with one. So if while play testing you see position 11 is the position you want, then you make the line of code above 10.
The other technique already mentioned is a simple SETPOS command, where you set the height (the z coordiante to the exact height above ground that you want to place the unit). You can put a unit anywhere using this command. This is how El Cojon stood on top of a Lamp Post (right before he lost his left jewel...poor guy...check out my Last Tango in Bagango mission if you don't know what I'm talking about).
unit1 setpos [x, y, z];
Rommel's tool for capturing coordinates is very handy. You should download it and use it. Saves hand writing coordinates. You can copy coordinates from his tool, and then paste them into an editor, and then paste them into your mission code later.
If this is all still a bit overwhelming, I can make a small example mission for you using the move to buildingPos technique, the setpos technique, or both. Just tell me exactly which building in which town.
You can zoom in the map and put a marker on the building then take a screenshot and post it here (and state which town its in).
Finally, you want these units to stay put, so the player has to hunt them, so you may want the following commands to keep them in their places:
doStop Unit1;
unit1 disableAI "MOVE";
unit1 setUnitPos "UP'; <-- use this if you don't want unit to go prone when they sense danger.
And most importantly, have fun!