Bad usage of Physics.OverlapBox - unity3d

Question

I don't understand the usage of method Physics.OverlapBox.
I want to put ten walls on a 4x4 plane in my scene. The width and location of the walls is calculated randomly. In the odd number of cycles in the creation loop the wall is rotated 90 degrees.
The walls presented in the scene should not collide with other walls... but it's not working.
void Reset()
{
int walls = 10;
for (int w = 0; w < walls; w++)
{
for (int i = 0; i < 5; i++)
{
float x = Random.Range(-20f, 20f);
float z = Random.Range(-20f, 20f);
Vector3 center = new Vector3(x, 1.51f, z);
int scalex = Random.Range(4, 13);
Quaternion quaternion = Quaternion.identity;
if (w % 2 == 1)
quaternion=Quaternion.Euler(0, 0, 0);
else
quaternion=Quaternion.Euler(0, 90, 0);
Collider[] colliders = Physics.OverlapBox(center, new Vector3(scalex, 3, 1) / 2, quaternion);
Debug.Log(colliders.Length);
if (colliders.Length == 0)
{
GameObject wall = GameObject.CreatePrimitive(PrimitiveType.Cube);
wall.transform.position = center;
wall.transform.localScale = new Vector3(scalex, 3, 1);
wall.transform.rotation = quaternion;
wall.tag = "wall";
break;
}
}
}
}

Answer 1

After your comment I think I now know what the issue is:
The physics engine simply doesn't "know" your walls colliders yet since the physics engine is updated in the next FixedUpdate.
You might want to call Physics.Simulate after each wall in order to manually trigger a physics update.
The docs are a bit unclear if it is necessary but you might have to disable Physics.autoSimulation before the loop and turn it back on after you are finished with the wall creation.

Answer 2

The solution proposed by derHugo (a lot of thanks) works from Start method. I added rotation to the walls. No collisions.
The code:
public void Start()
{
Physics.autoSimulation = false;
for (int i = 0; i < 200; i++)
{
createWall();
Physics.Simulate(Time.fixedDeltaTime);
}
Physics.autoSimulation = true;
}
void createWall()
{
float x = Random.Range(-20f, 20f);
float z = Random.Range(-20f, 20f);
Vector3 position = new Vector3(x, 1.51f, z);
Quaternion rotation = Quaternion.Euler(0, Random.Range(0,360), 0);
int scalex = Random.Range(2, 5);
Collider[] colliders = Physics.OverlapBox(position, new Vector3(scalex, 1, 1)/2, rotation);
if (colliders.Length==0)
{
GameObject wall = GameObject.CreatePrimitive(PrimitiveType.Cube);
wall.transform.localPosition = position;
wall.transform.localScale = new Vector3(scalex, 3, 1);
wall.transform.rotation = rotation;
wall.tag = "wall";
}
}