カスタムインスペクタに配列を表示するサンプルコード。

Sample.cs

using UnityEngine;
using System.Collections;

public class Sample : MonoBehaviour
{
    // member
    public int      m_Count;
    public int[]    m_CountArray = new int[ 4 ];
    public float    m_DeltaTime;
}

SampleInspetor.cs

using UnityEngine;
using UnityEditor;
using System.Collections;

[CustomEditor( typeof(Sample) )]
public class SampleInspector :  Editor
{
    // OnInspectorGUI
    public override void OnInspectorGUI()
    {
        // update
        this.serializedObject.Update();

        var sample = this.target as Sample;
        {
            // count
            sample.m_Count = EditorGUILayout.IntField( "Count", sample.m_Count );

            // array count
            drawArrayProperty( "m_CountArray" );

            // delta time
            sample.m_DeltaTime = EditorGUILayout.FloatField( "DeltaTime", sample.m_DeltaTime );
        }
    }

    // draw array property
    private void    drawArrayProperty( string prop_name )
    {
        EditorGUIUtility.LookLikeInspector();
        SerializedProperty prop = this.serializedObject.FindProperty( prop_name );
        EditorGUI.BeginChangeCheck();
        EditorGUILayout.PropertyField( prop, true );
        if( EditorGUI.EndChangeCheck() ){
            this.serializedObject.ApplyModifiedProperties();
        }
        EditorGUIUtility.LookLikeControls();
    }
}