I suggest you look at the command buildingPos here:
http://www.ofpec.com/editors/comref.php?letter=B#buildingPosMost buildings have them set, they are specific locations inside each building. For example I place a unit with the following instruction:
this setpos [7038.8,7147, ( ((nearestbuilding this) buildingPos 4) select 2) + 0.5]
in her init field. In the mission editor I put her on the building I want and the instruction puts here where I want her to be in the building. What I am doing here is moving her to a specific x,y location on the map and setting her height compatible with that of one of the buildingPos locations in that building.
You need to investigate where the buildingPos locations are for example by putting:
this setpos ((nearestbuilding this) buildingPos N)
where N is a number
In the init field of the player and seeing where you end up for different values of N