自分だけのPropertyDrawerを作ろう！ ref: http://qiita.com/kyusyukeigo/items/8be4cdef97496a68a39d

C#

using UnityEngine;
using System.Collections;

public class SampleScript : MonoBehaviour {

    public float hp;

    void Update()
    {
        Debug.Log( hp );
    }
}

Range2Attribute.cs

using UnityEngine;

public class Range2Attribute : PropertyAttribute
{
    public float min;
    public float max;

    public Range2Attribute (float min, float max)
    {
        this.min = min;
        this.max = max;
    }
}

Range2AttributeExample.cs

using UnityEngine;

public class Range2AttributeExample : MonoBehaviour
{
    [Range2( 0f, 100f )]
    public float hp;
}

Range2Drawer.cs

using UnityEngine;
using UnityEditor;

[CustomPropertyDrawer( typeof ( Range2Attribute ) )]
public class Range2Drawer : PropertyDrawer
{
    public override void OnGUI (Rect position, SerializedProperty property, GUIContent label)
    {
        Range2Attribute range2Attribute = (Range2Attribute)attribute;

        if (property.propertyType == SerializedPropertyType.Float) {
            EditorGUI.Slider (position, property, range2Attribute.min, range2Attribute.max, label);
        }
    }
}

RangeAttribute

using UnityEngine;
using System.Collections;

public class SampleScript : MonoBehaviour {

    [Range( 0f, 100f )]
    public float hp;
}

SampleAttribute.cs

using UnityEngine;

public class SampleAttribute : PropertyAttribute
{
    public bool init = false;

    public SampleAttribute ()
    {

    }
}

SampleDrawer.cs

using UnityEngine;
using UnityEditor;

[CustomPropertyDrawer(typeof(SampleAttribute))]
public class SampleDrawer : PropertyDrawer
{

    public override void OnGUI (Rect position, SerializedProperty property, GUIContent label)
    {
        if (sampleAttribute.init == false) {
            sampleAttribute.init = true;
            return;
        }


        ...


    }

    public override float GetPropertyHeight (SerializedProperty property, GUIContent label)
    {
        if (sampleAttribute.init == false) {
            return 0;
        }

        return base.GetPropertyHeight (property, label);
    }
}

SampleScript.cs

using UnityEngine;

public class SampleScript : MonoBehaviour
{
    [Range2( 0f, 100f )]
    public float hp;
}