NavMeshObstacle.size

Description

The size of the obstacle, measured in the object's local space.

The size will be scaled by the transform's scale.

using UnityEngine;
using System.Collections;

public class ExampleClass : MonoBehaviour {
    void Start() {
        AI.NavMeshObstacle obstacle = GetComponent<AI.NavMeshObstacle>();
        Mesh mesh = GetComponent<MeshFilter>().mesh;
        obstacle.shape = UnityEngine.AI.NavMeshObstacleShape.Box;
        obstacle.size = mesh.bounds.size;
    }
}