check if a position has a roof over it

so i am working on a gamemode that will have npcs spawning based on the nodegraph pos and player pos,

i would like them only to spawn outside but cant seem to find anything i can use to see if a skybox is directly overhead.
(i dont want the npcs to spawn inside of buildings)
The only thing i can find that seems like it could work would be http://wiki.garrysmod.com/page/util/TraceLine
This doesnt seem to work the way i want http://wiki.garrysmod.com/page/util/IsSkyboxVisibleFromPoint

and this is what i will be using for the nodegraph positions
http://forum.facepunch.com/showthread.php?t=1253175

Trace line will work for detecting if anything is above the player

can i check specifically for the skybox with traceline?

I also asked a similar question when I first started:
http://forum.facepunch.com/showthread.php?t=1324996

-Snip- Derp read it wrong