checking collisions before instantiating (not Physics.OverlapSphere)

I would like to check for a collision before an object is instantiated at the start of my game, for procedural level creation ‘road’ avoidance.

Currently I am using:

 	var oHit : RaycastHit;
	var objectPosition = new Vector3(Random.Range(-1.0,1.0) * length, 0, Random.Range(-1.0,1.0) * width);
  var checkResult = Physics.OverlapSphere(objectPosition, 10);
  if (checkResult.Length == 0) 	
  {place = Instantiate(object);

but it is not ‘accurate’ enough, and either avoids the objects entirely, or clips through them. the objects are complex and a simple sphere does not encompass them. I’d prefer a method that would use the mesh to determine collision.

I would like to use:

	var checkResult = object.rigidbody.SweepTest(objectPosition, oHit, 10);

  if (checkResult == false) 
  {place = Instantiate(object);

But it does not work in any way. it may be because I had to make the object a child in order to reset its transform values to zero for instantiation (like ‘freeze transformations’ in maya); thus it (the parent) has no collider?

for example:

objectParent(translate 0,0,0)

      |-object  (translate 3892,2873,972)

You can instantiate the object in an invisible layer and check for the collision if there is no collision change the layer on the fly and make it visible, otherwise destroy it.

I realize this is an old one, but I use a prefab that is essentially an empty gameobject with a sphere collider and script attached. I instantiate this prefab at the location I want to check. The script has uses Physics.OverlapSphere() in the void Awak() function. It seems to work ok.