MeshCollider.sharedMesh

Description

The mesh object used for collision detection.

If prior to setting sharedMesh any of the vertices, indices or triangles of the mesh have been changed then the shapes of the MeshCollider will be rebuilt.

using UnityEngine;
using System.Collections;

public class ExampleClass : MonoBehaviour {
    public Mesh meshToCollide;
    void Example() {
        if (!meshToCollide) {
            Debug.LogError("Assign a mesh in the inspector");
            return;
        }
        transform.gameObject.AddComponent<MeshCollider>();
        transform.GetComponent<MeshCollider>().sharedMesh = meshToCollide;
    }
}