I'm working on a script to place buildings and furniture sets. I need some way to determine if the ground(or the nearest colliding object in z axis) is flat enough. I've gone through ck wiki but haven't found any command to do that, i guess i can spawn some dynamically moving things and wait until they settle on the ground but that doesn't play well with the interface i have in mind and needs to be a lot faster. Thoughts?

This is actually a lot more complicated than you were hoping for. Getting a single Z position is fairly straight forward; shoot a projectile at the ground and record its impact z position in the explosion.

Getting the angle of the slope involves a lot more. You could take a look at Chesko's frostfall scripts, he includes some information in them.